The Uberschall just sounds like an overpriced, overhyped, glorified Recto to my ears. Granted, there are some differences, it's not the exact Recto sound, but it's quite similar. However, for me, that amp ONLY sounds good with a boost, without it, I absolutely hated it. I'd take a 2 channel Recto over an Uberschall any day of the week.
The 5150 III has much more usable tones and will compliment the Recto you already have much, much better IMO. It is significantly more versatile with an awesome clean channel and some great crunchy tones. It is much tighter than the Uberschall and a 3 channel Recto, with or without a boost.