The adaptors work, but I think there's a reason there's no brand-name production.
For the most part, supplying 18 volts to a power tool will make it work no matter what color it is. However, some brands have overload or overdrain protection built into the batteries, other brands put it in the tools. Sometimes batteries provide tools other information too like temperature sensing - or there's examples like Ridged Octane where you can supply 18 volts, but not unlock the "Octane" power boost from using the special batteries capable of higher power draw (similarly, Milwaukee HO).
That's not to say you shouldn't do it. You just might need to be more careful that you need to be with batteries and tools designed to work with one another. E.g. try not to drain batteries all the way flat, don't use adapters in really high-draw tools, stop if the pack gets hot.
Manufacturers don't want to create liability for themselves, nor do they have a desire to get sued for appropriating someone else's technology to make it work properly.
I have a few myself (Dewalt to Ryobi, Dewalt to Bosch, Dewalt to Ridgid). I would like to have other options than always using my Dewalt packs - I have a lot of Bosch batteries for example - the Dewalt adapters are by far the easiest to find.
In my ideal world, the battery and tool connections would be separate pieces and you could just connect them in whatever combination you needed.
