I find that they do hold up well, and honestly, I wouldn't put anything but calfskin leathers on my saddles....especially after investing in a brand new saddle.
Yes, they are very expensive. My Stubben leathers were $180.00 and the Amerigo leathers were $170.00, but you may be able to find them a bit cheaper than that. Take care of them properly, and they should last a long time....and be less abrasive on your saddle flaps.
Of course, this is simply my opinion/experience. Others may chime in with theirs.
"The best and most beautiful things in the world cannot be seen or even touched....they must be felt with the heart." - Helen Keller