Margin-trading is what provides the real reward and potential in daytrading bitcoin. You will be able to access the leverage to profit well from relatively small moves in BTC/USD price. High risk, high reward, high potential for loss. However, you need not use Futures only to speculate, hedging on lower leverage is also a great use case for Bitcoin derivatives if you just want to defend your coins. 
In the course of managing the Fund’s investments, ProShare Advisors will need to periodically adjust the Fund’s holdings in order to maintain investment exposure approximately equivalent to the Fund’s assets. This process entails obtaining additional inverse exposure as the Fund experiences gains, and reducing inverse exposure as the Fund experiences losses. The higher the volatility of the bitcoin futures contracts in which the Fund invests, the more such rebalancing can adversely affect the Fund’s performance.
It’s reasonable to assume that a product named a future is attempting to predict the future. For Bitcoin futures, this is definitely not what they deliver. The core utility of the futures markets is not predicting the future prices of their product but rather the secure delivery of a product at a known price, quality, and date. If there’s product seasonality (e.g., specific harvest times) or foreseeable shortages/abundances then future’s prices may reflect that but neither of these factors applies to Bitcoin.

(a) derive in each taxable year at least 90% of its gross income from (i) dividends, interest, payments with respect to certain securities loans and gains from the sale or other disposition of stock, securities or foreign currencies, or other income (including but not limited to, gains from options, futures, or forward contracts) derived with respect to its business of investing in such stock, securities or currencies, and (ii) net income derived from interests in “qualified publicly traded partnerships” as described below (the income described in this subparagraph (a), “Qualifying Income”);
Securities (including short-term securities) and other assets are generally valued at their market value using information provided by a pricing service or market quotations. Short-term securities are valued on the basis of amortized cost or based on market prices. Futures contracts and options on securities, indexes and futures contracts are generally valued at their last sale price prior to the time at which the NAV per share of a class of shares of a Fund is determined. Alternatively, fair valuation procedures as described below may be applied if deemed more appropriate. Routine valuation of certain other derivatives is performed using procedures approved by the Board of Trustees.
"We expect that the futures exchanges, through information sharing agreements, will be monitoring the trading activity on the relevant cash platforms for potential impacts on the futures contracts' price discovery process," CFTC Chair J. Christopher Giancarlo said in an official statement. "This includes potential market manipulation and market dislocations due to flash rallies and crashes and trading outages."
Fixed margin will isolate your margin to the individual position you have made in an instrument. So if you have 1 bitcoin in your account and you put 0.2btc margin for a Weeklies Futures long position, and it gets margin-called, you still have the 0.8btc left. However, if you're on cross-margin, also known as portfolio value margin, then your whole balance on the site is going to be used to back all your positions, and if you get margincalled, it's because you have run out of money on your whole account.
Those who believe in Cryptocurrency claim it to be the next big thing in the history of mankind. The mere fact that Cryptocurrency is beyond the control of any government body gets it a lot of eyeballs. Imagine a universal currency beyond the control of liquidity, inflation and government subsidy. This would mean that the commercial activity of economies working on Cryptocurrency shall be privatized absolutely.
Market conditions should be considered favorable to a Fund when such conditions make it more likely that the value of an investment in that Fund will increase. Market conditions should be considered adverse to a Fund when such conditions make it more likely that the value of an investment in that Fund will decrease. For example, market conditions that cause the level of the S&P 500® to rise are considered “favorable” to the Ultra S&P500® and are considered “adverse” to the Short S&P500®.
Crypto Facilities and the CME Group  have been calculating and publishing the Bitcoin Reference Rate (BRR) since November 2016. Such an official rate is a prerequisite of options trading in the traditional markets. The BRR is calculated based on the rates from the biggest exchanges: Bitstamp, GDAX, itBit, and Kraken. More concretely, it is calculated based on all Bitcoin vs. USD trades on the participating exchanges between 3 and 4 p.m. London time. To calculate the BRR, the hour between 3 and 4 is divided into 12 intervals of 5 minutes. For each interval, the volume-weighted median of the Bitcoin price is calculated (statistically, the median, in contrast to the average, prevents single outliers from distorting the price). The BRR is then the average of these 12 median values. More details about the calculation of the BRR can be found in the BRR whitepaper.
Disclaimer: Trading carries a high level of risk, and may not be suitable for all investors. Before deciding to invest you should carefully consider your investment objectives, level of experience, and risk appetite. The possibility exists that you could sustain a loss of some or all of your initial investment and therefore you should not invest money that you cannot afford to lose. You should be aware of all the risks associated with foreign exchange trading, and seek advice from an independent financial advisor if you have any doubts.
In this guide we don't want to deal with social loss risk, so use the FCA-regulated, London-based bitcoin derivatives exchange CryptoFacilities. They offer contracts with 2% margin requirement (50x leverage) as well as a 15% margin requirement (6.5x leverage). They are 100% bitcoin based, but they don't accept US customers. Sign up here to get started: