There is not normally a reason, unless you did not install the castle nut appropriately, to deal with that in the field. This is really for your go bag to carry into the field to address problems there rather than install tools.
I understand if you do not want to purchase a bunch of tools to build but all in ones are kinda like a jack of all trades, master of none and as a result, using these without caution can mar your new build's surface, damage parts, cause you to lose parts, etc. A simple castle nut wrench of decent quality runs about 7-8 bucks and has flash hider, etc. wrench to boot. In the field, a flat tipped screwdriver or punch can work with a hammer to get a castle nut off or put one on (more difficult) if you are careful. You can also buy some alternatives to using a castle nut when adding your buttstock and buffer tube anyway. The AR was designed to be easy to maintain in the field with minimal armorer type tools and folks have proved ingenious to getting around cheaply through homemade and expedient tools. There are quite a few youtube or webpage sources on how to make most of the stuff if you are so inclined. Wheeler, like most of the other sources below, are pretty much made with Chinese steel so there is not a whole lot of difference in quality between it and generic Chinese stuff you find on Amazon, etc. If you want the higher grade stuff, go to somewhere like Brownells and THR posters can point you in the right direction on specific tools such as one for dimpling gas keys etc.
Full disclosure here, I have some Wheeler made tools but also some from other sources including Brownells etc. The Wheeler stuff is average in quality and I would rate it for occasional personal use rather than intensive.
Depending on where you are, you might be able to get a loaner tool. Most of the rest of the stuff, apart from the bolt scraper, such as the torque bits etc you could get elsewhere for cheaper in a small screwdriver set with a better handle. Here is one for 7.99 for example,
https://www.cdnnsports.com/51-piece-screwdirver-kit-outersrgunsmith.html?___SID=U
The A2 front sight adjustment wrench is not much use if you do not have that and a separate tool is cheap or you can simply use a bullet tip. Here is a cheap homemade tool and how to make one,
https://www.instructables.com/id/Homemade-AR-15-Front-Sight-Adjustment-Tool/
You would be better off to get a set of AR punches which are pretty cheap for takedown of both the upper and lower receivers. For about the same price, you can get all of the punches, a hammer, and a bolt disassembly tool for $30 bucks at Amazon
https://www.amazon.com/Grip-AR-15-R...=ar+punch+set&qid=1554997758&s=gateway&sr=8-4 By the way, the bolt disassembly tool is really one of the those few tools that I do not care to use cheaper alternatives in getting out the ejector and its spring.
And the bolt scraper's utility is marginal--a cheap set of brushes including bronze ones, specific bolt scraping tools, or even use of gun cleaning solvent soaking plus some sort of home made scraper which can be made from a variety of materials can be made. One is made by simply crushing a brass cartridge and using the edge to scrape. Personally, I prefer the Avid but others are around as well that do a good job for a little more dough.
In the field, where weight is a premium when toting it, multi tools can be useful because the stuff that I named won't necessary pack in a neat lightweight package. On a build at home and for maintenance, all in one tools represent a compromise in being more difficult to use than the proper tools and increasing the chances, which you may not mind, of marring the surface or damaging some of the parts.
End of the line, its your money and time, your choice, but better tools usually make a job easier than making do with lesser tools.
