Its mildly upgraded by TM Hi-Capa standard, but functionality-wise you should not be disappointed with the gun. Only real upgrade they did is fitting the slide, the springs(hammer and recoil) and installing the hi-flow. With guarder's parts for those you are looking at probably less than $100 USD in "upgraded parts". For $160 total its not bad...

About the slidelock, if you shoot 2 handed(and a righty) the slidelock is where your left thumb would be, so that's not much of an issue IMO, and I've learned to do the pull-back on the slide to release the slide on mag change...Hi-Capa can be a big pistol though, especially if you are starting from Glock or something....