My old man has a typical old mans back and lacks muscle at his wither when he is less fit so has a front riser for that purpose at the start of the season, once he is fitter I have to watch it as he does even out and I can go without it. However this year he changed shape so much as he was fitter than he has been for years and we had to change to a rear riser and a new saddle. Nothing is simple with this man! It does make all the difference though as if I get it even slightly wrong and take it off too early you can immediately see him getting uncomfortable.
the master saddler i use (fitter to GB event team etc) told me that in the Pliance pressure testing they did, the best results they got were using the Prolite. since then, i've used them a lot.
they do wear out after a lot of use, they lose their springyness and need replacing, this seems to take years though...
saddle needs fitting to take prolite into account, obv!
I use the all in one I think they call it, comes in numnah or saddle cloth, brilliant, I started using mine when my horses back was sore after doing a fun ride, now I use them all the time I have two, one to use while the other is being washed. I love it that the back stays dry because of the special stuff, dri-lux or something, my horses back stays dry. Approx £65 but well worth it IMO