Thanks!
Bubble King Double Cone 180 with RD3 Speedy pump.
So I got a FedEx box from aforementioned "random Kijiji guy".
I opened the box, and found this inside:
Hello,
Best wishes on your build, hope everything goes as planned. As far as the skimmer goes, I have the same, but I believe one size larger, mine powered by the eheim 1262. You will not be disappointed, this is simply the best performing skimmer I have used yet. Like most skimmers, set it to your sweet spot, and watch the collection cup grow daily, great skimmate, and luckily for me, I have to overfeed to keep NO3 up.
So this is skimmer number two. It is an Austrian-made (not US version) ATB 840 Econo Small with Eheim 1260 pump - well to the best of my research that's the model anyway.
Compared to the skimmer inside the Royal Exclusiv bag, this ATB doesn't look very impressive - though I can see the design is smart. The very large bubble plate and smooth skimmer body all the way up to the top of the skimmer appears as though is should provide as non-turbulent flow as possible, so this is promising. This is the first ATB skimmer I've ever seen in person and I'm interested to see how it performs as some people claim it rivals the Royal Exclusiv skimmers.
The sump on my 50-gallon tank isn't big enough to accommodate the ATB, so it's having a vinegar bath right now. Maybe I'll haul it down to the shop and put it in one of the FO tanks and see what it does.