I have tried Jelly Pantz and I approve :)
I have been using Jelly Pantz every time I ride for at least 3 months now-- I ride a variety of horses and use a variety of saddles. I mainly do dressage and also jump a little. I didn't want to comment until I'd tried these for awhile, but now I can say that 'Yes' they work for me!
It could be that with the right horse and saddle, I wouldn't need these but some of the horses I ride are very bouncy and being an amateur, I don't always stay glued to the saddle.
I also use KY jelly, which works well WITH the Jelly Pantz. Before I started using Jelly Pantz, I would actually get rubbed so much that I would sometimes bleed and would definitely be sore from friction (now I know it was probably friction between tender skin and my regular panties). I would 'recover' in a few days, but certainly wouldn't want to ride again the next day. This didn't happen all the time, but enough to make me search for a solution.
I did not have the problem that some of you have with the seams of my panties rubbing, so not sure if this would be the solution for you if that is the problem.
I think the jelly pantz help me stay in the front of the saddle and on the right part of my seat for dressage. Otherwise I'd want to lean back a bit to 'protect' myself.
Hope this helps!