I did it a couple of months ago and it was an evening's worth of work with Netflix on in the background. Not infuriating at all, but there were definitely a couple of sweaty palm-inducing moments. That said, iFixit's instructions and pictures were faultless. If Apple doesn't release a MacBook Pro refresh that addresses some of the widespread concerns (touchbar and keyboard, notably), I would have no hesitation about swapping the battery again in another few years.
In short: it didn't take too long, but it was still a pain.
Most people seem to take the shortcut where they don't completely remove all internal electronics before peeling off the battery. They just try to be careful to not have the acetone touch the plastic speakers (which would melt in the process.) It's not super complicated, just scary.
I didn't think it was too bad. I tend to enjoy these types of projects though.
I did manage to puncture the battery slightly at one point, Luckily I thought ahead and let the MBP drain to ~0% to reduce the chance of a lipo related fire. So nothing happened. I wasn't gentle about removing it, if you took the time to properly heat the glue and pry carefully it could be done with no drama.
How much of a pain in the ass was separating the glued-in battery from the chassis? iFixit makes it look infuriating