I have more BBQs than bikes at the moment, from one that will spit roast a 50kg pig down to a mini "briefcase" one, I do quite a lot of BBQing
The answer to your question is, it all depends. Mostly, on what space you have, and what your bbq tendencies are. If you have sufficient space, I would get one charcoal and one gas, for when you want instant outdoor cooking without fuss. I would expect that it will take up no more space and cost about the same. For a gas one, Cadac are my goto brand, the one* I have for our caravan (Cari Chef 2) is very hard to beat (£200-ish). Add to that a Weber (again my goto if I was to only have one, because of the heat control) and you're set. They will work better than the combo, no doubt, although what I've seen of one was actually quite good, with gas flame isolation.
If having instant heat is important, and you don't have the room or inclination to have two but still want the charcoal option, then the combos look appealing.
*(OK, one of the two Cadacs I have, the other has a cast iron plate and is no longer available)