Years ago, dive tables were the only option. Today, the majority of divers dive with a dive computer and it makes sense.
The computer tracks your depth, bottom time, speed of ascent, and no-decompression limits in real time. Tables can't do that. If you change depth during a dive, it updates. Tables are set before you get in.
Watch-style computers are the most common go for these days. These are compact, readable underwater, and you'll use them as a regular watch between dives. Console models are still around but fewer buyers go that way now.
Basic computers go for around $300-odd and cover everything the average diver would need. You get depth tracking, dive time, no-deco limits, log function, and usually an entry-level freediving mode. The $500-800 range adds wireless air monitoring, improved screens, and additional nitrox compatibility.
The one thing buyers forget is conservatism settings. Some models are more cautious than others. A conservative setting means less bottom time. More aggressive algorithms allow longer time but with less safety margin. Both work. It just what you're comfortable with and your diving background.
Talk to the find here staff at a dive shop who dives with a few different models first. Staff will give you real-world feedback on what's good and what isn't marketing. The better Cairns dive stores put out gear reviews and comparisons on their websites too