My LBS (Goldtec) lent me one of their XX1 style chainrings to try out and see how well it coped without a clutch mech. I bolted it to my XC race bike (didn't shorten the chain to match as it was only temporary) and headed off to Llandegla expecting to spend most of the day putting the chain back on.
It did fall off, but only once! That was on a smoothish bit of trail where I landed a jump and immediately back pedalled to lean into a corner. All the rockier stuff (e.g. the section just after the blue splits off after the long first climb) where I've had chains fall off before passed without issue. I Strava'd my way to 3rd overall on the first black descent and 6th overall on the newer black B-Line section near the end so wasn't hanging around either.
I did another local ride last night (fast XC stuff, no major rocky bits but some fast descents with roots, lots of steps and a downhill sprint across a ploughed field!) and it didn't miss a beat all ride. Having messed around with various chain devices over the years, I'd say this was perhaps just as successful as using a proper device, but much better looking!
I have begrudgingly bit the bullet and ordered a clutch mech, but only because I don't want to worry about dropping a chain during an XC race. If you just ride casually with mates, I'd definitely recommend giving it a go!