Okay so I took a look at the Red Sea Nano. First be aware of the reported leak issues with Red Sea branded tanks. To be fair though, I believe a large majority are in the bigger tanks, not the nanos. I could be wrong though. Leaving personal biases aside:
Generally Red Sea equipment can be used on other brands of tanks. However, in this case the Nano Mat, is 3.5x3.5 foot print, so it won’t fit the JBJ.
Also, I see the ATO is built in on the Red Sea Nano XL, this to me limits the size of the RO reservoir but can be convenient for limited space (unless I’m completely mis understanding their system). My experience with ATOs is the reservoir is a separate “tank” typically under the stand or next to it and just the small sensor is in the main tank/sump area.
With all that said, the Red Sea has some nice features, such as the filter sock (though that gets replaced by the Nano Mat if you go the roller mat route).
The built in protein skimmer, again nice feature, not sure how “built in” it is though. If it’s removable then great for cleaning, if not, not that great of feature due to cleaning hassles in my opinion.
Some other brands to consider just for AIO purposes are Innovative Marine, WaterBox, Cade, and Planet Aquarium Tideline. Each have their own features or lack there of. Each have pretty decent reputations (can’t say I’ve seen many if any leak issues reported).
Something to consider, if you have a LFS, many of the brands (including Red Sea and JBJ) now have “map pricing” which effectively eliminates the ability of the retailer to advertise a lower price than what the manufacturer allows, so possibly consider buying from the LFS instead of online if you can as they’ll likely be the same exact price. Gaining that friendship with the LFS may “help” in the future with purchases too. You never know.