I've used that salon system one before.
Pros: wax is quick to apply, isn't too hot to hold, wax doesn't come out too thickly, don't have to squeeze to disperse wax.
Cons: Plastic holder sometimes breaks when replacing wax cartridges, doesn't stay hot for very long and takes a while to heat up (you would probably have to have up to 3 on the go for a full leg wax), it can be difficult to clean properly, I find this wax makes the skin very sticky after and doesn't always get all of the hairs off, also because the temperature doesn't remain constant, there is a higher chance of the wax sticking to the skin or any dry areas as it cools down.
Now I just stick to using pot wax and spatula, I can do it just as quickly and don't have to worry about temp change and can get all the wax off the skin easily with none left behind, so I actually find it a lot less messy. I feel like using a spatula is more precise but it's a case of each to their own!
If you really want a roller wax kit, I would suggest looking at something like a roller wax heater where you have the cartridges sitting in a heater and take them out to use. Then you can have a bunch on the go and have the option of different sized cartridges and different types of wax (such as creme). Good luck, it's fun to try something new.