CRP-5 & E-6B differences
E-6B doesn't do specific gravity, it assumes gasoline weighs 6 lbs per US gallon. CRP-5 does, you can use local value, but it is usually .726 or so for avgas, Jet-A is about .8. The CRP-5 will also give you fuel weight in kg in one calculation.
Ergo, CRP-5 can be used for any airplane, anywhere, E-6B is best for piston engine airplanes in USA, but still usable anywhere else.
Accuracy is about the same - the larger CRP-5 makes it slightly easier to read, but remember the real-world figures you base your calculations on may not be totally accurate to start - the 8 GPH might actually be 7.9 or 8.1, the 20kt wind could easily be 15 to 25, and so on.
E-6Bs are much less expensive, as cheap as $12.00, made of the finest grade of aviation rated cardboard - aluminum ones are about $30, and with most of the E-6Bs, the *instructions are printed right on them!!!!* which is a brilliant idea!
The "instruction booklets" are awful and will make you want to take up surfing instead of aviation . . .
I teach this stuff in ground school - a little practice makes it easy.
Best Regards,
Echo Mike