I've just signed up for this for the month's trial, so will see how it goes - after that, £50 seems pretty decent value for a year. Like yourself, I still buy way too many discs, but doing this might prevent me from splurging on Arrow titles whenever they go on sale. Plus, it's much more convenient than hunting around for ages to find the right disc...
I've done that a couple of times. Managed to keep it to stuff I know stands up to a few viewings but it's very tempting to gamble on stuff as their sales spiel is pretty good.
Just been looking at their site and they're steadily putting more 4k stuff on disc so hopefully the streaming service will follow suit. I think the new UHD of Tremors might be a purchase when the next sale comes around.