Hi
I have a hive double pot digital heater - one 1000 pot has warm wax and the other 500 pot has hot wax. It's been fine, has a lid too and both pots can be set for different temps etc or just one on at a time. I went for the double one as I do mobile and didn't want to carry 2 separate pots about, they do do single pots though in 500 and 1000 sizes. Hive pots have been around for years and get a good review on here. Hopefully you won't need to have 4 pots on the go with the digi ones.
I used to use phd system - loved the hygiene aspect of it but did so much waxing that I got through lots of tubes - which are quite expensive once you add in delivery etc - so wasn't as cost effective as the pots are.
Hive have their own site, and Ellisons and Beauty Express sell them too.
The pots seem to keep a good temperature, and they have a fast heat up setting too which is useful.
Hope that helps.
Choccy x x