If he's serious about tech, or if you want absolute top of the line, the Petrel might be the only way to go.
HOWEVER, it's drastically overkill for the VAST majority of divers. I mean, WAY too capable. Cheaper computers work just as well (some may say better) for a more recreational diver (as opposed to technical). My experience is to stay away from Suuntos. The way that they do their calculations is really goofy. The computers I've used and liked (both together being crucial) are actually on the lower end of the price scale. They do everything I need in recreational diving (and then some) but they don't have useless bells and whistles or the associated price tags. In so many things, simple is the way to go.
Having said all of that, the Hollis DG03 is a fantastic computer for the price. It doesn't have the best screen, and is a little goofy to use, but it comes with a "Quick Start" guide and good instructions and is simple once you get the hang of it. The Oceanic Geo 2.0 is more user friendly, better screen, but smaller. It's also more expensive. My wife dives it and ADORES it, you can't get her to get rid of it. It's "watch sized" (big watch) but we don't use it as a watch-replacement, just as a dive computer. I think those two are of the best computers on the market in that price range. These pale in comparison to the Shearwater Petrel, but they come with less than half the pricetag.
As for letting your SO choose for himself, that could go both ways depending on him....and you obviously (hopefully?) know him better than we do. I would not want my wife to buy me a dive computer unless she knew PRECISELY which one I wanted, but I'm super picky. I also enjoy doing the research (I'm a geek
). My wife wanted me to get a list of good ones, and she'd pick hers after a
brief explanation of pros and cons (and after she got to look at the pictures and prices).
As for features you want: Nitrox is a requirement, and you had might as well get one capable of 99% or 100% oxygen and at least 2 gasses (3 is easy to find for cheap as well). Not that he'll be using those soon, but the computer could become a good stop-gap if he decides to go tech. Wireless Air Integration (AI) is a feature some love. I feel it to be dangerous as it makes you complacent and trust your computer too much. It's also one more battery to keep up with, and one more thing to fail. Others love the ease of getting all of their information on one screen (time, temp, air, depth). Wireless AI will all have a higher cost associated with it, and the transmitters (that send the data) are expensive as well.....but it's worth it to some people.
