Looking at the description the mobicool unit looks more suited and the cheaper ones get poor reviews. I think I know we should get the mobicool unit but has anybody used either or similar?
I dont think the cheaper one you show would be up to the job, theres a Kampa one here for £12.99 which is designed to run coolboxes. We have an Outwell one, it works fine, but they do get quite warm as the current draw is fairly high.
I am not very knowledgable about electricity, but the one I have is a small box, like the more expensive one you show. It has a cord from cool box to adapter and then another cord to the three pin plug to go into the EHU (all usual warnings about use only purpose built units, RCD protected etc!). The adapter itself is a small box that has a carry handle. As has been mentioned, it does get hot, so I keep it away from the cool box on the rationale that the cooler the air around the camper, the cooler it can keep its contents.
the camping gaz/coleman one is what we have and it also runs other 12v stuff that works from a cigarette socket. they were in decathlon last week for about 20 quid