The Syno's that I quoted are amongst the smallest available, around 60mm SL, so they should go fine in a 10g tank.
However, I think Oto's are probably a better choice, if nothing else because they are compatible with just about anything that isn't big enough to eat it. And they are easy to get...
The syno's also need to be kept in a group, so they offer no big difference there. The cat-eLog doesn't say anything about eating it's tankmates, so I don't think that would be a problem.
I haven't got a clue as to availability of this particular specie of Syno's. Some of the bigger species of Synodontis will grow to over a foot in length and are suitable for 100g+ tanks, but will outgrow a 10g tank quicker than a student blows his weekly allowance on beer.

[Perhaps not really, but it seemed like a fun way to express the fact that they aren't suitable for a 10g tank...]
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Mats