In the Amazon comments there are warnings about it.
You sure? Youtube and Soundcloud set the final volume , no? What level for mixing? Then What level for mastering? Then what tool should I use to make that level?
Back when cds ruled the world, the mix was just the mix. The overall volume didn't make any difference as long as it wasn't ridiculously low or clipping. You would take all your mixes to a mastering engineer who would put the songs in order, do fades, set the time between songs, set overall eq so all the songs sound like they belong together, and set the final volume for each track so that all the songs flow from one to the other and to the standards of the genre at the time.
Now that everyone is essentially doing singles, album flow is no longer an issue. But the final volume and overall eq needs to be done as a separate process. You have enough to worry about just getting a good balance during the mix, trying to master at the same time will have you chasing your tail forever.
Don't bother looking at your lufs meter during the mix. It doesn't matter at all at that stage. As long as the mix doesn't clip, you should be good.
After you render the mix to a file, import that file into a new reaper session. The most common tools are a compressor, eq and limiter. You won't necessarily need all three. The compressor and eq setting should be pretty gentle. The compression is there to glue the mix together, not really change the sound of it or catch peaks. For me, 2:1 is a really high ratio in this context and 1-2db of reduction is a lot. Eq should also be gentle at this point, maybe a wide bell and half a dB or so to shape the mids or lessen a problem area somewhere. The limiter will be the thing that gets you your final volume. It should be placed last in the chain. For maximum volume, you simply turn down the threshold until the mix starts falling apart, then back off a bit. (Auto makeup gain should be turn on for this) That will be as loud as your mix can go, if it isn't loud enough, then you need to go back to the mix and fix whatever the problem is.