Let's not beat around the bush... This was designed to be as close a representation of the classic Tube Screamer circuit but affordable at the same time. Did they pull off both? Well it's certainly very affordable, far less than even the least desirable versions of the TS, and massively cheaper than a TS9 or an actual TS808 (The version this is a clone of).
As for the sound, it's pretty close in my opinion. The build quality is very good for the price, but far inferior to an actual TS. So you may be sacrificing durability for the price unfortunately. Saying that the pedal is pretty tough, mines been thrown around and dropped and obviously stamped on, and the sound quality is just the same as when it was brand new.
Bare in mind that you may be more likely to find increased variability in the tone from unit to unit. If you must have the full, unadulterated tone of an original TS808 and nothing else, then you may get a unit of this pedal which is 100% like for like, but you may get a unit with very slightly different components inside it, the effect of which may or may not subtly affect the tone to a noticeable degree. This company trys to use 100% like for like components in their circuits where ever possible, and from what I've read most of these pedals should be identical to the circuits used in the TS808. However they are producing these pedals ridiculously cheaply, and therefore at times if they can't aquire the EXACT components they usually put in it you may end up with a unit that is very slightly different in its sound. Things like using 1/8w resistors in place of the 1/4w or higher components used in the TS808, different value capacitors (albeit very close to the original circuit) and so on. How much these variations will affect the pedals tone, that is hard to say. But chances are for most players, especially those who lack the resources to purchase an actual TS808, you'll likely not be able to tell the difference and neither will those listening to you play.
So in summary, unless your a professional, gigging musician who is at the level where such subtle effects on their guitar tone is important enough to justify the much bigger cost of buying an original TS808, this pedal will do the exact same job and do it very well.
If you want a Tube Screamer but can't afford the cost, buy this and you'll be just as impressed with the results... and even more impressed with the amount of money left in your bank account after the purchase.