Years ago, dive tables were how everyone dived. These days, most divers use a dive computer and for good reason.
A dive computer monitors your depth, bottom time, speed of ascent, and NDL in real-time. Tables can't do that. If you move between depths during a dive, a computer adjusts. Tables are set before you get in.
Watch-style computers are the most common go for at this point. cairns dive computer guide They're small enough, easy to read, and you can use them as a watch too. Console computers are still around but not as many buyers go that way these days.
Budget computers go for around $300-odd and do everything most divers requires. They give you depth, bottom time, NDL, dive logging, and sometimes an entry-level freedive function. The $500-800 range gets you transmitter compatibility, improved readability, and extra gas compatibility.
What buyers overlook is conservatism settings. Some computers are more cautious than others. A conservative computer means shorter bottom time. Liberal settings allow longer time but at reduced buffer. Both work. It comes down to what you're comfortable with and experience level.
Talk to the staff at a local dive store who's used a few different brands before buying. They'll give you a straight answer on what's good versus what's marketing. Decent dive shops publish product guides and comparisons on their sites too