I bought a similiar unit off ebay w/out the spigot and non-didital. It is handy and I use it to heat sparge water. I also use it as a boil kettle but I supplement w/ a heat stick. Bottom line...they are nice units at the right price. I paid 50 bucks free shipping. Others I remember pruchased at H Depot for like 30 bucks on clearance. Handy unit but nothing to build a brewery around. They heat pretty slow. I fill mine, power it up and go do something else for an hour or so.
I also use an 11 gal ss bayou classic propane turkey frier. having done both, I can say that niether gas or electric is superior...both have their merits.
Whew. sorry i followed the hijack and ignored the orig. question.
I would say 2 heatsticks are required for a 6 gal boil. Of course this varies as to the ambient temp, kettle insulation, etc. 3-5000 watts.