I have a number of Koralia 240's and one may overpower a 10 gal. They're great circulators, but have a fairly high velocity output. In comparison, the larger Koralia 600 has much more flow, but it's not as much of a jet (that's way too big, though, flow and physically large). The Nano 450 is definitely too large, it can push water across a 4 ft tank. I don't use circulators in any of my tanks any more, but multiple 240's were OK in bigger tanks, the 450's seemed to move water through the plants too fast, making algae a problem.
Hydor has some very small pumps I've used in dead corners to keep build up down and those are about right for local circulation, their effect dissipates a foot or so away.
We have 3 betta tanks, 2 eheim Aquastyles, 6 and 9 gal, and a 6 gal fluval edge.
The edge has an AC 20 which is kind of an odd filter in AC's line. I love AC's and they are the only HOB's we have (9 of them). With the 20 turned down halfway and a lot of frogbit in the tank and a sponge on the inlet, it works OK and isn't too harsh. Suction isn't very good though and when the sponge starts loading and it can almost stop flowing. The AC 30 won't do that even with an extension on the intake tube. If you watch it, the AC 20 will work OK, we had the same issue with plants until the tank was loaded with floaters. The betta in that tank lounges in a tangle of frogbit roots right in front of the filter output, there must be a dead spot near the surface.
The eheims don't have any issues at all with flow, their internal corner filters are very gentle and our guys can perch in watersprite in the opposite side of the filter corner and sleep all day!
I think sponges work best in betta tanks, but with CO2, probably not a great idea.
Other than the diffuser, AquaTop makes some decent corner filters that may be OK, the smaller ones have gentle output and they're all inexpensive. The tiny Tom, etc., canister with a spraybar doesn't move much water, their pumps are not too strong, whether you want to experiment with one, IDK.
An entire world is in your tank.