Otos might work singly with a betta.
Once I posted about wanting to put several Otos in a 10 gallon tank with my betta, and here is what I got
1: Otos should be kept in groups of 3 or more because they get stressed in smaller numbers and are socially dependent
2: If Otos are kept in smaller numbers than 3, they will get too stressed out and may suffer and die (Oh noes!!!)
3: Otos need a 10+ gallon tank, so your 10 gallon should be fine IF you are just keeping it with a betta.
4: Otos are always looking for a meal, so if you want to leave a lot of algae growing behind your plants and decor, that would be good. They should always have a snack such as veggies or algae wafers (make sure your betta doesn't find these--he will gorge himself on them, being the piggy that bettas are)
5: Lightly plant the tank: there should be almost a solid wall of plants in the background. Then lightly plant the front and you'll have tons of fun watching the fishies prowl around in there....hehehe.
6: Put as many Otos in your tank as you can support--NOT too many though, remember that it will decline the tank's quality and will make the fish suffer!!