I’ve been experimenting with 1×9 this last week using a 32T chainring and 11-32 cassette and one of Superstar’s XCR £17 chain devices.
It looks much the same as Sir HC’s E13 and futon river crossing’s mrp above.
Initial impressions are very good. After a bit of fettling with BB spacers to get the device in line with the chainline I’ve been loving it. In four rides I’ve not lost the chain and there’s only a tiny bit of rub on the device when I’m in the 11T at the back that I will try eradicate when I can be bothered.