Many (most? all?) of the cheap tube pres are cheap solid state pres with a subtle 12ax7 fuzz circuit in them. That is, they're NOT tube pres. That's understandable, being 50x cheaper than a Manley, great river, etc.
My advice is, if you like the sound, fine (always true). If you want one as a different flavor in addition to your other pre(s), even better. But think pretty hard before choosing one over a cheap mixer like a 4 channel Mackie or Soundcraft. Even the newer Behringers have gotten some good press. The pres on these have gotten very good as all 'round cheap & cheerful useable gear.
The cheapest tube pre I'd rely on as my *only* pre would be the Peavey VMP2, running around $700 if they still make it. That's a nice piece of gear.