Both of my parents had cpap machines. I think the hardest transition was having the masks. Also, if you’re lovey dovey and roll over to cuddle, the house will likely be in the way…
My husband has one. It's actually pretty quiet and makes more like white noise than anything super disruptive. It wasn't a big transition for me at all. For him, he tried a bunch of different masks before he found one he liked. He did a lot of research about CPAPs and their usage online. It ended up being a huge improvement for us. He only has fairly mild sleep apnea, but once he started using the CPAP he needed less sleep. He used to nap pretty much every Sunday afternoon, but once he started the CPAP he felt so much more awake and alert and didn't need the Sunday nap anymore.
There really isn't a smooth transition. The new models now days are so much quieter but it's still a fair amount of noise and you'll have to adjust to it. He may struggle with it at first as the only way to find the right mask is trial and error. For example if he opens his mouth it'll cause a vacuum suction and if he does that a lot you may need to tell him about it and he may need to go try one of the full face ones. Between having a new sound at night (which is very bothersome for the people who like it super quiet), something on their face, and a hose. It's an adjustment that only time can help.