This is a massive simplification, but High Gravity essentially uses a 'dimmer' to scale their heat up and down. This forces you to raise and lower the heating element- fine tuning it over the course of the day. The electric brewery uses PID's which broadly speaking- are a set it and forget it system. That is, you dial in 152 and you should get 152.
If your goal is "boil", then which ever is cheaper is better. If your goal is fine temperature control of your mash, I wouldn't bother with HG. I'm sure guys will stand up and say there system works just fine, but the power of a working PID is the ability to establish consistent temperature every time.
I have a PID controled RIMS tube and I'm still working on it. I have some issues, but I'm all in. I love my gear (all built by me) and wouldn't brew without it.