Fowler was considered decent enough starter tools back in the day, when you didn't have the moola for brand name tools at maybe 2-3x the cost. Some of it was actually very good value. Maybe an analogy was Craftsmen back in the day - a Sears sticker but an bigger actual manufacturing name behind it (maybe Rockwell saw or Dremel depending on the tool). Most of the value there was the warranty though.
But today with so much easy access to offshore stuff, its so hard to know what you are getting. I have an entry level Fowler gage block set purchased on sale which suite my needs perfectly. But the DTI I had maybe 15 years ago was a waste of money POS - sticky ratchety needle movement, bezel kept popping off, crude accessories. IMO if you are going to gamble on used, try to stick to a brand name. At least it will have started out life as a higher quality tool, but all bets off if it was used hard or dropped or any of the usual gotchas. You can potentially spend a lot of effort & money machining a part, the last thing you need is second guessing the physical measurements. That's not a good area to cheap out, but just my personal opinion.