I used to use the H-gate shifter in the appropriate cars, until my shifter started missing shifts a lot. For example when I shifted from 2nd to 3rd it would remain in neutral in-game even though the stick was properly in 3rd. Probably a bad contact somewhere. It got so annoying that I switched to sequential shifting
By now I'm so used to it I think it would take quite a bit of practise for me to become used to the H-gate shifting again.
Maybe in the future I'll buy a seperate shifter from ATC Labs (I think it is?), they're supposed to be of much better quality than the G25 one. But there's loads of other stuff I want to spend my money on first, and I actually don't even
have a lot of extra money to spend, so that'll probably be a while.
As for advantages... I guess sequential shifting is
easier to shift fast, but with some practise you can shift an H-gate just as fast.