I only had the opportunity to use one a couple of times. A friend in Montana had it. It was awkward to handle and sucked ergonomically.
I will state up front that most of my dislike for it comes from its looks and for me awkwardness to get into position. That mag coming out of the top, creates a completely different balance point than anything else I've tried. I also didn't like the hot casings ejecting onto my hand from the ejection port, just in front of the trigger guard. It's a good thing the front hand grip is strong, it most definitely plays a big roll in controlling the smg. If your hand slips up to the barrel while shooting, the barrel is very hot.
Now for the good points. I liked the selector switch. Very positive, with three positions. Full forward = full auto. 45 degree = semi auto and 90 degrees = safe. It is also a relatively heavy smg. Heavier than a Sten and the barrel brake really almost eliminates muzzle climb while firing bursts. Even with the rudimentary sights, which are way to small and flimsy for my taste and make acquisition in low light almost impossible, it is very accurate out to 50 yards or so. Even though the top feeding mag makes it awkward to control, the top position makes it extremely easy to change out a mag. I liked the stock but there was way to much drop for my body type. Maybe Aussies all have really long necks. Also, it isn't the least bit fussy about ammo. We tried some 380 acp in it without one failure to feed or fire. That is saying something for it. NO, it wasn't one of my brighter moments but the curiosity bug was biting.
IMHO, the Owen is very reliable, awkward and robust. For taller shooters with long necks, it would fit them much better than me. The top feeding mag can be distracting but with practice that wouldn't be a problem.
The model I used had Bakelite grips, I believe others had wood grips.
IMHO, the biggest problem with the Owen is that darn top feeding mag. It does make it nice to use from a prone position though. The mag sticking up like it does, also makes it a pain in the butt to carry. If you have to go prone really quickly, you stand a good chance of getting the mag butt jammed in your face or neck. A side fed mag/ejection system is far preferable. IMHO, the side feed is likely one of the best methods designed for feeding/ejecting ammunition in an SMG.