It's well worth a go, if you feel you have any issues of timing and tempo, such as timing glitches or rushing and dragging.
If your rhythm is wonderful and everyone agrees, doesn't just sound good to you, then some musicians don't need a metronome so much and in many traditional music cultures metronomes aren't used. So don't feel you have to get one, but it is worth a try to see if you get on with it.
You can get a metronome for your PC or laptop, many are free downloads. Also some on-line metronomes that run in the web page.
I maintain a big list here:
http://robertinventor.com/bmwiki/Big_list_of_Windows_and_Online_Metronomes
It's for Windows and online, also has links to a list of apps for iOS.
You can try my Bounce Metronome too, if you have a Windows machine, the free taster in the download is completely free yours to keep and the visuals help you to keep time.
http://bouncemetronome.com/features/free-taster
The mechanical metronomes look nice, but most are limited because they only do one tick sound. Some of the software and online metronomes are much more versatile,
You can set them to many different sounds, can set them to play the first beat of the measure in a different way.
With my Bounce Metronome the bounces across the screen also show your position in the measure, and you can also set it to bounce in conducting patterns, and count beat numbers visually.
You can also set it to go silent briefly to test your timing, a useful exercise in metronome technique (this is in the paid for version of Bounce), and gradually changing timing.
The electronic digital ones are also more versatile too.
Not true that they are less accurate. Your PC clock is based on the same technology as a digital clock. So long as you don't have some heavy task (maybe a full disk anti virus scan or similar) running on your computer at the time, it can be very accurate to about the nearest millisecond.
Techy note, it is actually possible to go to sub-millisecond accuracy as well with special techniques and programming. It is rarely done though as it can limit the range of sounds you can use, harder to program, and in practise you are unlikely to notice any difference between a metronome that is accurate to about a fiftieth of a millisecond, and a metronome accurate to a millisecond or so.
Even when you have heavy CPU use in the background for some reason, that used to disturb the timing on older computers. However, on a modern computer with multiple cores etc then it normally won't make any difference to the timing either, and on a modern computer it is pretty hard to disturb the timing of a software metronome. The timing of video streamed over the internet can be dodgy at times, but that's a different issue.
A mechanical metronome needs to be wound up periodically and slows down and stops towards the end when it runs down, though it can run for a fair while before it runs down.
A mechanical metronome can be very reliable, but I wouldn't say it is more reliable than the electronic or software ones. Though some software and electronic metronomes may be unreliable if badly programmed or something not quite right in the electronics / progarmming of a digital metronome.
In short, you can start with a free online metronome or downloadable software metronome. Then you will find out if it is useful and what you can use it for.
If you feel you need something else at that point - the most likely reason is so you can carry it around with you more easily than you can with a laptop. In that case many musicians get an iPod app or similar.
Or you can get your mechanical metronome at that point if you are still keen on the mechanical type. Some musicians still use them, and just like them better :). Fair enough.
You might find my page here about the vanishing click useful, though it may be a lot to take in if just started.: http://robertinventor.com/bmwiki/The_Vanishing_Metronome_Click_-_Burying_the_Click
Also there are books on metronome technique. The basic idea is that you can work with the metronome in separate exercises to help with your inner sense of rhythm and sensitivity to musical time. That may work better than actually trying to play your music along with a metronome, for various reasons. Then just play your music with the metronome occasionally, or to deal with tricky passages.
The reason is that the natural way humans play rhythms doesn't exactly match the regularity of a metronome or click track. So you can't really fit the two styles of playing together, at least for most styles of music.
There are musicians who attempt to do so by playing their music to a click track, they do manage it more or less with some small discrepancies usually. Some like the sound, but many listeners would say music played to a click track is not so interesting to listen to, or dance to, as music played in a more natural way.