Performed the upgrade myself, with a bit of patience and a wole lot of 'cussin, I was greatly rewarded: the tone is smoother, has better low end than it originally had, more sustain is generated, etc. ...
With my trusty Les Paul Special re-issue (outfited with Seth Lovers) I experimented the Tube Screamer through my Zoom 503 amp simulator ... who said singing sustain wasn't possible through solid state again? Through one of the Zoom's "Boogie" patches I was frazzled and amazed: the sound is powerful, smooth and sustains like a charm.
I did notice some random noise whenever I used the neck or bridge humbucker on its own, but that can also be due to my on board electronics (the hum would go away if I gently tapped on the micro switch on my guitar).
Overall, I have a better, sonically improved pedal, and it was dirt cheap: $1.75 in replacement parts!
A plastic casing is a plastic casing, and I would definitely feel a whole lot better about it if I could retrofit the circuit board in a metal casing (say, a crappy pedal like a Guyatone or a Tokai - but the pots, jacks and foot switch wouldn't fit properly ...).
Re-assembling the pedal I've found the foot-switch to have become a bit more temperamental (I need to give it a deliberate, sharp press for it to stay on and the same to switch it off). Mayhap that the switch on the board isn't properly aligned with the pedal switch, and that's easily fixed.
That said, I'm no Trash/Punk/Grunge freak, and with proper care, the pedal should be durable enough.
This pedal has gotten an attitude adjustment and a personnality change, it's improved 100%. For those overdriven - sustainy lines (David Gilmour, steve Hackett and Carlos Santana come to mind) it's definitely the ticket.
I'd still say that if you can afford a TS-9 classic or a TS-9 re-issue, go for it: those pedals are definitely sturdier. If you're on a tight budget and are well skilled with a soldering iron, the TS-5/808 mod is an option. As always, trust your ears above all.