Not that much of a learning curve. If you an type on a keyboard properly you can pick it up very quickly.
Benefits are that its faster and a things like QCF or Z motion inputs are super easy. But unless you really spend time grinding it out and learning all the trickery of it, like the negative edge stuff and input buffering on movement, then there is no actually in game benefit really and it will all come down to personal preference.
10% of the time is nothing. And a reasonable amount of time to mess up an input.
This has everything to do with being a newbie. He says he sometimes gets an additional input before or after getting the double button press. This indicates that the system is reading one of the buttons a little early or a little late. Which means he is pianoing the inputs, or releasing one button slower than the other.
I too find the inputs easy as I have also played a couple games. But I have a mate who can't get it down no matter what. People are different, let it be. You may have had some issues with your stick. I can't say if that is legit or not. As I haven't had any issues with the sticks you have mentioned. Or any others I use at the gaming meet ups. But it doesn't mean everybody is having the same problem. And I just feel it is not in the OP's best interest to be told that it's his stick. As that could be a cop out to not practice anymore and blame it on the hardware.
In you other post you mentioned you tried the UFB and had the same problem. That's an indicator that it isn't the stick. The "stick" is the PC board that is inside of it, removing it and using a UFB means it is now a completely different product. The buttons and the joystick used are the same in the old boxes as they are in the new boxes. I use a UFB in my own stick and have had zero problems.
Same people may be having issues. Some may just need to practice. And since we don't know what the person on the other side of the PC screen is experiencing, the best answers we can give are to practice. And advise on what could be causing the problem based on technique. At the end of the day it wont hurt the person asking. And if it turns out they do have a faulty stick, they still got all the necessary practice in that they should have been doing anyway.
I second Darkstalkers. If Nintendo could lock that down as their exclusive fighter it will kill. MS has KI, Sony has that other game, Nintendo could shine. And hopefully it will make its way to Evo and boom, cult following wanting in and Nintendo sells a bunch of Switches.