I found the thicker grip more comfortable on some workouts than the standard bar size. Some other workouts however, I had to take them off to get better grip.
As for the strength gains, my assumption is due to needing to squeeze the stiff kind to grip the bar or dumbells. This causes tention in the entire arm while doing the reps. The research covers bar size, but not the extra squeezing throughout the workout. Does it produce more strength? I don't know because it is too early for me to say and my strength is going up anyway before I used them.