Welcome to the BA site, Frank1955. I have not used any Mr Beer kits to know the answer to your question, but Mr. Beer questions do come up occasionally in the Homebrewing forum. Jump on over there https://www.beeradvocate.com/community/forums/homebrewing.8/ and pose your question and see what kind of conversation you get.
Welcome aboard! As @Mothergoose03 advises, the Homebrewing forum is where you'll find an answer to your question. Meanwhile, there is an old discussion on the topic here. Cheers, and good luck!
Sung to the tune of Mr Plow, "Mr Beer, that's my name. That name again is Mr Beer." Welcome to BA, OP. Cheers!
Welcome. I actually got started in this hobby with Mr. Beer and used the keg for a few years. You may find the trick now is in making your own extract recipes or finding recipe people have put together and fermenting them in your Mr. Keg. https://www.brewersfriend.com/ is a great tool for creating recipes or changing a recipe you find to meet your equipment needs and limitations. Long story short, yes, you can use any sort of extract in your Mr. Beer. I actually have been thinking lately about how I wish I kept my keg for small batches. But I will say the ingredients and extracts from Mr. Beer leave a lot to be desired, so by making a few tweaks, you can make great homebrewed beer with Mr. Beer. Also, definitely check out the forums on homebrewtalk's website. I'm pretty sure they have recipes with the Mr. Beer sized batches in mind, as well as a separate Mr. Beer forum or sub forum. Good luck, cheers, and you're going to love this hobby.
I brewed for a couple of years with the Mr. Beer fermenter. I never used the extract kits they provide except for the two that came with the fermenter itself. My local homebrew store had a big book of their own designed recipes with extract and minimash versions. For the two years I used the Mr. Beer kit I just halved their 5 gallon recipes and went with it. The beers were slightly stronger than the recipe was created for but they all turned out just fine. If you want there are plenty of 5 gallon recipes and you can just divide the ingredient list in half to where they would be for 2.5 gallons but just brew it to 2 gallons to fit in your fermenter or you can divide the ingredients by 2.5 and you will have very close to a perfect recipe for the 2 gallon fermenter. For example: If a Pale Ale recipe calls for 6 pounds of dry malt extract (DME) you can divide 6 by 2.5 and use 2.4 pounds of DME to get the same beer out of the Mr. Beer fermenter. Or you can just use 3 pounds of DME and get a stronger beer. Looking at Beersmith 6lbs of DME could yield a 5.15% ABV beer but if you use 3lbs in Mr. Beer it'll be around 6.5%.
I usually have much better luck using Google to search the BA forums than using the built-in BA search box.
I started brewing with Mr Beer extracts. It's simply a vessel in which to ferment wort. I brew all grain 5 gallon batches now. The last time I used Mr Beer keg was about 4 months ago to ferment a second runnings pale ale. Try using the beer smith app, you can load recipes for Mr Beer and also create 1 gallons n recipes. Northern Brewer sells 1 gallon kits that can be done in the Mr Beer keg/fermentor.
