It’s good that you have a rabbit savvy vet as that will keep the risks of something happening very low. Of course if you’re not completely comfortable with it, there’s no harm in cancelling the appointment for now til you’ve done a bit more research
Usually when people say that their bun’s personality changed its because their bun was super hormonal and possibly aggressive/territorial and once the hormones have disipated, they become ‘nicer’ because they don’t have the hormonal impact. So if your boy is already lovely and not very hormonal, there’s not really anything that could change so don’t worry about that!
I think buns can develop hormonal issues when they get older if they are unneutered but I’m not too sure about that so I’ll wait for someone else to chime in. There is also a risk of testicular cancer, I don’t know the statistics but I believe the risk is much lower than a female’s risk of uterine cancer, but it is still a risk nonetheless. There’s also the issue of not being able to bond easily in the future if you decided to get another bun.
In my personal experience – my Peanut had a very quick recovery. I was told that he started eating within 10 minutes of waking up from the anaesthetic and apart from not being as active that first day/night, he was totally fine. A neuter is MUCH simpler and less invasive than a spay and because of that it’s also a much quicker procedure (so he’ll be under anaesthetic for less time than a female would)
I personally would neuter him. If anything, to avoid the risk of developing testicular cancer and to allow the option of bonding him in the future if you wanted too. But as I said, it wouldn’t hurt to cancel/delay do a little more research.
Oh and as your vet is rabbit savvy, you must already know but just in case, DO NOT fast him before his surgery. A bun must never be starved prior to surgery.