The combiners do work but please understand that 50amp services provides you with 2 separate 50 amp legs or a total of 100 amps of service.
The combiners send 30 amps to each leg (or in your case 30 amps to one leg and 20 amps to the other) for a total of 60 (or 50) amps. That's still way better than only 30 amps but you have to keep your eye on what things are on which leg of service to ensure you don't trip on breaker or the other.
I should also add that if the 2nd connection has a GFCI plug or there is a GFCI in the circuit then the combiners will NOT work.
