There is no 510 "model" or brand except the Joye 510, which is one of the older mini e-cigs. 510 is a thread pattern. It just tells you what battery will fit what cartridge or cartomizer. Big mods use it because there are zillions of accessories that will fit on it. It's the most universal thread pattern.
I had a Joye 510 when I first started. That was the best mini-cig out there at the time. Nowadays, I wouldn't recommend it. There are better options for not much more money. If you want something like a mini-cigarette, good and simple, you can't do any better than a Volt by SmokelessImage.com. It's not a 510, but it's the best of the best mini-cig types.
If you want something that's a 510 type with a little bigger battery, the kGo is a good option, about the size of a Sharpie Marker and it'll last for a day or more between charges. It is a 510 type and also accepts accessories that are made for the eGo e-cigs. It's probably the most popular model for people to upgrade to when they get tired of swapping batteries all the time on their mini-cigs. It's a little less expensive than the Volt and uses cartomizers, so it also is a simple 2 piece e-cig. You fill the cartomizers yourself.
This one includes 30ml of juice and 5 cartomizers w/free shipping for $45
Elite Vaporworks KGO Starter Kit with Boge LR Cartomizers - KGO
Those are the two best choices for simple, reliable and inexpensive upgrades from the Blu or safe cig.