It should also be easier to reverse-engineer a userspace driver by just watching what it does. What is *really* nasty are binary drivers with a dependency on a specific (usually 3-years obsolete) kernel version.
For example, I bought an expensive ($500) fast 32-bit parallel I/O card 4 years ago, which claimed to have Linux support. This turned out to be "but only on RedHat 7.3 with the default kernel". In the end, we threw out the hardware. Actually, we replaced it with another "Linux-supported" hardware item, called a QuickUSB. This also had only a binary driver, but it used libusb, and we were able to reverse-engineer it to write a GPL-driver. (But it still wasn't good enough in the end).
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