There are 2 synthetic saddles in my barn, and both have held up woderfully for years. I'm not familiar with that saddle specifically, but I wouldn't worry that it is cheaply made. Just be aware that it is not leather. My Abetta cordura saddle has held up fantastically for over 5 years, and with a spray of the hose looks like new, but I don't expect it to last for 50+ years, as I might expect well cared for leather to do. Who knows, in 50 years I may be very surprised! It's not a workmanship question, it's a material life span question. Check the tree materials and fit, of course.
Is the saddle new from the manufacturer, or is it secondhand, never used (as the note kind of reads)? I would buy it. For $100, you can gamble and replace it in a few years, or eBay it if it isn't what you were looking for. I wouldn't worry about the workmanship, though.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown