i imagine all zinc based products will be good, but electrox has had some very good reviews that others have not. yes it is more expensive, maybe it is the same stuff but I have peace of mind knowing I am using the same stuff that has worked very well in reviews and tests.
1969 Four door Saloon Old English White 1275 with ported head and HS4 carb. Wolseley 1500 front brakes. Currently off the road with a leaky master cylinder!
I've just broke the bank and gotten a tin of Teamac zinc rich primer for the princely sum of £20. Way more than I'm happy about, but way cheaper than Galvafroid and if anything a slightly heavier tin (it weighs an imperial shedload).
Seems to go on OK, but was a pain to stir as well as a pain to the now very thin wallet... (But not as much of a pain as burning out my grinder and discovering a lot more hole where metal should be)