This type of anaesthetic is far safer than an injection. They can slowly increase the dose until your rat is asleep, whereas once they inject something into the body if its too much it would be too late. The earlier you spay the better, the chances of your girl getting a tumour later on in life are probably higher than any risks from surgery, just find a vet that has some experience with rats and you'll be fine
Well... There's no doubt that there are health benefits, but be prepared for a few things!
-Some rats will be fine with their stitches, and some won't. Many people will tell you as long as they have pain killers and antiinflammatories, they won't pick at them...... I woke up at 3am because my girl had ripped out her stitches. She had somewhat dehisced, but I was able to beg someone to watch her and take her. They then gave her staples. They had to wrap her with an adhesive bandage to prevent her from bending over so she cannot get to them.
-Make sure you have nothing to do the day or two after to keep an eye.
-Many people will tell you that their cage mates won't bother the stitches. In my case, my girls like to play rough/energetic, so I tried but it wasn't happening. By the time she gets her stitches out, she will have been separated for two weeks. So, get a ONE LEVEL hospital cage for your baby.
As far as the gas/safety of the procedure ask the vet all info you need: Have they done many spays? Have they lost any rats recently? What is their success rate like? etc etc... That part should be fine
I will be making a post at some point entitled: Things that can go wrong after a spay/surgery since I think almost every thing that could go wrong did for my girl! lol
When my girl got spayed she was stitched up with internal dissolvable stitches, so there was nothing on the outside except a line of bumpy skin. The only time she touched it was for cleaning it up and she didn't pick it once, a spay wound is completely healed after 10-14 days. What you could do is separate her for a minimum of 7 days and then if the wound is looking okay let them free range together under tight supervision. Try to minimise her activity for the first 4 days, and then after that just keep an eye on her until you get to about 10 days.
If you get them spayed together you can keep them together during recovery. I got mine spayed together and when I brought them home they bounced back within hours of the spay, I was surprised. See if you can get your vet to use glue/internal stitches and not regular stitches or staples.