Admittedly I never used it, but when people talk about getting someone MrBeer, I usually talk them out of it. It unfortunately doesn’t give you much versatility. I think their schtick is to sell the kits and lock you into their odd batch sizes. The beer should be fine, but you’ll outgrow MrBeer pretty fast if you really get into the hobby. I would suggest trying MrBeer a few times and get the hang of the process, and then move onto a larger, more “standard” equipment.
Most recipes expect you to be able to deal with 5 gallon batches, and usually any deviation from that is 5+ gallons. I think MrBeer’s 2 gallon batch sizes would be annoyingly small, basically yielding about a 24-bottle case of beer; except for the weight factor, brewing more at once is almost entirely the same amount of work. Anecdotally, I think larger batches taste better. A scientific reason might be less exposure to oxygen per unit of beer.
That said, you should be able to use a proportional amount of the various ingredients to fill the MrBeer fermenter. However, some words of caution: they seem to use a proprietary malt extract that is pre-hopped. Their proprietary extract might be designed to assure reduced residue from hops. If you start doing your own recipes, adding hops separately, there’s a good chance the MrBeer system’s design would be prone to clogging, which risks both messy explosions and, more tragically, contamination.