When you're fly fishing for trout & other similar fresh water fish (like bass, bluegill, etc) the reel typically functions mainly as a holder for your fly line. Drag systems need not be intricate or complicated (naturally this is a different case when deep sea fishing or other large game fish pursuits).
Now, there's noting wrong with using a more modern fly reel with a more complex drag system if that's what you like, but for trout fishing you don't really need it. To that end, you might want to look at used, classic 'click & pawl' style reels.
The video below sums all this up very well. I like the presenters concise thoughts on the matter & I agree with him on this issue. If you're looking for a good fly reel for your trout fly fishing, than by all means take a look at some classic reels.