For the "budget stuff", my main problem so far is EXTREME inconsistency in specs and quality.
If I get a surefire or a klarus of a particular model, and then get another one a few months later, etc...they will be about the same in performance and quality. They are consistent.
If I get a SRK, or a DRY, etc, and then get another one, every single part of it might be different. The specs for the earlier ones might be better, and then you get XML instead of XML2's later on, or thinner walls, or different drivers, and so forth, with no change in the published specs.
So I try experimenting with these in case I find ones that DON'T break if I drop them, etc. So far, they break if dropped...and my "good lights" don't break when dropped.
They can be fixed, reinforced, and or souped up typically though, so its sometimes worth a shot.
Vinh for example can take a crap light and replace the weak springs and thermal paths and so forth, and pot the electronics, swap in a real LED, etc...and make the el cheapo's actually useful in real life. As they come from the factory, most are mere toys. They do produce light, but, not according to any formula you can count on...and not after being dropped, etc.
If I USE a light, it has to be reliable and sturdy, AND produce light.
So, If you do mod a cheap/budget/value light to make it work for YOU, it can be rewarding. A little solder and some TLC can restore the VALUE part of the equation.