There are APV (advanced personal vaporizers, which are advanced ecigs with features like VV or VW), and there are mechanical mods. Mechanical refers to the machinery. It will always work so long as you replace the batteries, because it is an independent mechanical device that doesn't rely on screens, propriety batteries/threading, or any other internal mechanisms. It is simply metal.
Generally speaking, people get mech mods for their durability and because they are unregulated. If you build your own coil, for example, and it clocks out at .8 ohms, most devices refuse to fire that. A mech mod has no inner protection, however, and therefore you can vape low resistance heads and build your own coils etc. If you're just looking for an upgrade, I would suggest an APV rather than a mech. I have been vaping on a Vamo V2 Stainless for about a month and a week now and I love it. It was a great 'first step' upgrade that allows me to see the resistance on the head, switch to VW, and has a better battery life (depending on the batteries you buy) than the 1300 Spinner I started off with.