I just got one delivered to me friday night. So here's a pretty comprehensive review/experience log. This is my first flat cage.
I would say it's literally not a good fit. The ring size is perfect, and I love the way the locking system works (barrel lock), but I got the wrong sized 'head', I thought I would need a large, but when locked in place, the bottom of it clamps down too deep into the top of my balls, a smaller top/head (which was select-able when I ordered it) would have definitely made it more wearable, lesson learned.
Mine came with a straight 3 or 4" metal catheter, I've been interested in sounding and since it was optional use I figured why not. I used lube and inserted it all the way in without any issue. Also worth mentioning that I was semi hard, so the catheter didn't go to the base and it didn't hurt or anything, it was definitely an odd but not unpleasant sensation. Anyways, I calmed back to flaccid and re-inserted it while attached to the rest of the cage and this is an inverted model, so it literally pushes the entire penis inside of my body. When I got to the very end of the push, I felt a bit of pain at the end-point of the catheter, I was really cautious and moved my hips around and yep, sharp pains if I moved certain ways, so I removed it immediately. I'm sore, but not injured fyi.
Anyways, after that, I tried the cage without the catheter and got it on relatively easy, and tested out the 'tease factor', meaning watch some porn and see what happens when I get excited.
It felt nothing like my Vice / mini, but I didn't expect it to. Getting hard apparently is still possible, and it's extremely uncomfortable, it tries to push out on the cage and since it can't, it starts growing sideways-ish. Hard to explain, but it just felt like I my dick was going to bend in half if I continued to excite myself. I can't imagine actively playing with others with that kind of risk of injury.
All in all, I think my interest in flat chastity is satiated, it's interesting but nowhere near worth breaking my dick over it. I'll stick with mini chastity and maybe try out the 'nub' series next.