I can't think of any real cons so to speak. I would use a spa heater for the greater surface area to prevent scorching if you plan to direct-heat the mash or with extract. Plus you need a good size heater, 5kW+ and you need a 220VAC circuit to power it because in my opinion, the SS mass of a keggle will dissipate quite a bit of the heat.
Hmmm, Right now I'm thinking about going Electric only in my HLT and maybe MLT. I don't think I'd want that direct contact w/ my wort in the boil kettle, that just seems like scorch city. Thoughts?