Some folks do use the Marigold stuff as a substitute, yes. The low salt version's the best one. But bear in mind that this isn't strictly speaking on the allowed list - you'd be better off with the Cambridge stuff, really.
I have a little bovril gravy with my veg, as this is the only way I can stomach it. My CDC said this was ok and I dont think its effected me, but you can never be sure. I am happy with my losses so far.
Although I am not saying it wont effect you
x