Dynamite engines are definitely great little budget engines, I'll vouch for them any day of the week. They have great power too. Like GreyWolf said, they are built by SH, who makes engines for a lot of companies, and those are really nice engines IMO that put out a ton of power. The Big Red is a beast, it puts out close to 4hp, so you better make sure your drivetrain can handle it. I learned pretty quick (with an SH .28 p8) that you can demolish cheap steel dogbones and swingshafts without even trying.
Reds is an Italian company, I think they've been around but as of late they've been putting out a lot of new stuff. There's a lot of .21 options from various companies, some of them are pretty pricey, but for your Revo, unless you're doing a big block conversion, you'll need either a Dynamite .19 or O.S. .21, which just drop right in. I have two TMaxx's with Dynamite .19 engines in them, and they have been great engines that are really snappy. Even my all aluminum truck has no trouble pulling wheelies. The (mostly) stock chassis with the .19 is pretty insane how fast it is. Apparently rumors are that nitro MT's are back in vogue a bit (though I highly doubt we ever see the level of the TMaxx Era), so maybe we'll start to see some more MT specific applications. It's a shame about Novarossi, from what I understood the pandemic caused a supply chain issue and being a small family company they just packed it in. Maybe they come back later, I don't know - but they were very popular and well built engines for a good price.