Our store got 4 Self Checkouts in a 2 x 2 grid during our Home Innovation remodel. The first month was awful, and it was a pain adjusting your closing routine as a GSA with all of the added steps, but once your team gets to know them and they are working well they are a valuable asset. We schedule a couple of cashiers under "Guest Service Training" for monitoring SCO, and it seems to work fairly well. They are very useful at night and in the early morning, when people are making quick purchases and just want to get out of the store.
The only reason why closing them is a pain is because there are a lot of steps, so it easily adds 30-40 minutes to your closing routine if you have to juggle closing them and dealing with other things, which is often the case. When I closed, I would call for my start funds at around 10:45 (My store closes at midnight) and I'd usually have my funds by 11. Close the back two SCOs by 11:15-11:20, then close Food Ave/Starbucks/Pharmacy, then close the remaining two SCO's, then work on closing the remaining register except for 4 or so until the store is completely closed.
When they fuck up, it can be a pain to fix. Especially when there's an issue with the coin/bill accepter or the dispensers. I've had to call the Vendor to resolve the issues a few times, and only once did we need a technician to come on-site to get it in working order again. I placed the call at around 8PM, and the technician arrived around 9 or so which is really quick, given that it was already evening and I wouldn't have been surprised if they waited until the next day to come in to fix it. Guy fixed it and was on his way 15 minutes later.
No issue with that here, the SCO's are a godsend for meal breaks.