Nova Extreme T5 High Output X2 Lighting Fixtures > Freshwater > 24"
2F/2Bulbs fixtures
I'll be the first person to tell you to not get an Odyssea fixture, and the first to recommend fishneedit.com when it's possible.
Both fixtures listed above are about the same price and much more powerful than the one you posted, there are a bit longer than a standard 10G but once on the tank you can barely notice the overhang. 2-bulbs also will give you a great range of corals to keep from softies/polyps to LPS and even some SPS
For the 20G long standard ones are 30" in length I believe and I'm not sure on other brands but I do know fishneedit.com sells a 2-bulb and a 4-bulbs fixture in that length. Same applies, 2-bulb will be great and a 4-bulb even stronger.
Once the bulbs go out look into getting either ATI, KZ, UVL, or Giesemann T5 bulbs, they are a bit pricier but they are the best on the market in terms of PAR and life