I've owned a Glock-version Sub-2000 Gen 1 for 20 years, and also had a Gen 2 and later sold it. Fired several hundred rounds out of them.
Honestly, it's light-duty. The latch mechanism for the folding action is polymer. It's not rare to see them cracked under varying levels of use/abuse. Never happened to me, but after enough reports, I save the gun for emergency use only.
It's neither easy to operate nor fun to shoot. The "iron" sights are set rather low considering the straight-line stock/recoil spring tube, and acquiring a proper stock weld takes work. And once you do, you get whacked every shot as the steel recoil tube is right on your cheekbone, not under it.
The controls, especially the cocking handle, are difficult to operate and in an inconvenient position. The crossbolt safety works opposite of every other crossbolt safety.
The front sight is light duty and difficult to adjust on the Gen 1; on the Gen 2 it's merely wiggly (un-solid).
Mounting a RDS on this firearm is an aftermarket Rube Goldberg style affair which also defeats the purpose of the carbine as being lightweight, compact and simple. Maintaining zero with any of the RDS mounting options is crop shoot.
Recoil is substantial for a 9mm, since it is straight blowback and a light weight firearm with a nice hard checkered polymer buttstock. Also, do not entertain the thought of ever completely disassembling this firearm. It is a collection of screws and small wound springs and other small miserable components that you will regret trying to re-assemble.
Having said all that, it is reliable. Never had any kind of a malfunction with any 9mm ammo.
I have a PC Carbine - which is not without it's own set of Ruger-level fail - but I shoot that a heck of lot more often, and I think it's the better choice if you don't require lightweight.
The Sub-2000 has it's share of fanboys who mostly are into "cool gadgets" and spend an equivalent sum of the purchase price in various aftermarket accessories, the end result being no more capable than the stock original. It's like buying a Mini-14, and a bunch of aftermarket items, and when you are all said and done, for the same money you could have purchased a more capable AR and a whole lotta ammo.