We are giving you a little information here to lead you towards the right questions to ask to help you when buying a scuba diving computer, so that the computer fits your needs. We would recommend that you talk to your diving instructor about what kind of diving that you would like to do, and then they can help you by asking questions to see where your future in diving will take you, and what your dive gear needs will be .
For myself I have 1000 dives and I don't do tech wreck diving. I do travel a bit and I don't always take all of my dive gear with me. I am also a PADI and SSI instructor, so on most dives, I have divers that I am leading or teaching courses to, so I like to have my dive gear setup quickly, to give me more time to supervise my divers. When I had a strap on computer, I was forever forgetting the darn thing, because I was so use to my Oceanic computer that was on my gauge package. I never forgot my computer but it was not a good setup if I wanted to travel light, with just my mask and computer. When I became an instructor, I decided to upgrade again to a Suunto Stinger. The deal is this, as you go along; if you are seriously in to diving, you will upgrade your dive gear just like I have, so don't feel pressured to buy the latest and greatest right from the start. If you take care of your scuba equipment it usually will retain allot of resale or trade value.
Most times if you rent scuba gear they don't have compasses so I upgraded again when the Suunto D9 came out, which added a compass and air integration. I also like it because like the Stinger, I don't have to bring my "regs" out to give dive log details, when it comes time to fill in the logs. Even better the D9 has a USB interface and I just click a button and it tells me all sorts of cool stuff, like how much air per min I am breathing, which if you get into cave diving or cavern diving, or just want to plan some deep dives, gives you a good idea of how much air you are using for planning your dive profile. The electronic compass is also nice for when I am navigating at night in a strange town, and I don't speak the language like Saigon or Bangkok, so for me while the cost was high, I get lots of good use out of it. A neat added benefit is that it marks you as a diver so you get to meet other divers because of your dive watch.
Number of pieces
If you are a weekend diver having your own computer is nice because you are familiar with it and you know how to use it. Diving can be sometimes stressful and not knowing the computer intimately can add additional stress to your dive, just like diving any other new equipment, except that computers tend to take a bit more to learn on the front end. I myself got into some trouble when my computer batteries ran out and I needed to rent a computer, and didn't understand all the messages that the computer gave me, resulting in me going into decompression diving and not knowing it! Needless to say going into deco and not knowing it could have been very dangerous.
I recommend to most weekend divers that they look at the Suunto Gecko with its large easy to read face or if you like a watch look at the Suunto Mosquito another one with a bit more aesthetic appeal would be the Mares Nemo. All 3 of these are god value for the money and they hold up well
If you do a lot of diving and you are thinking of going down the advanced tech wreck diving side talking to a tech wreck instructor will have you ask questions like will I be doing multi gas$%: Am I an aggressive diver$%: Am I fit$%: If you are just starting down that path you might look at a Suunto Viper or some of the Uawtec line which allow some deco diving. Some computers will violate you and turn into gauges, not good as it could end your computers use for 24-48-72 hours. Your best bet is to talk to the tech wreck people before buying dive computers for the more advanced diving.