The enclosures are actually kinda fine... they're pretty thick ABS. Being plastic it still feels cheap and creaky, but they're fine.
And the parts inside are basically the same kinda thing that Boss, etc uses. The plastic doesn't offer any shielding, though. And they can have noisy bypass sometimes, for whatever reason. Probably has to do with filtering on the digital pedals that they don't have down as well as the more expensive stuff (or just don't care).
Anyways, here's basically what you can expect:
Guts! by
McSpunckleFX, on Flickr
The digital ones almost certainly have more SMD parts and such, but the pots and switches will still probably be through hole. You can replace the bypass switch with one of those momentary soft touch deals and keep the stock bypass, or hunt down the FET switches, jumper them, and wire up a regular true bypass switch.
The biggest problem is gonna be the size of the PCB. They're bigger than they need to be (to fill the enclosure) so that gives you a bit less room. You shouldn't have any issues sticking it in a 1590BB, though.
It's basically exactly the same procedure as rehousing Boss pedals. I'd, personally, probably go with painting the plastic enclosure with shielding paint and find a way to stick a true bypass switch in the stock box. BUT, I get why people hate the plastic.