I've just switched from spiro mittels to innovation 140Hs. Its hard to know exactly what the difference is as I switched at the same time as getting a new, higher bridge, and a new soundpost, but I'm very happy with them.
They feel quite similar to play in terms of diameter and smoothness, slightly lower tension. The sound is lovely, in my opinion, already quite mellow after only 2 days, but still with quite a bit of sustain. The note sounds to me to have much more fundamental centre than many other strings, which is really nice and makes for improved inntonation.
This seems to be a good time to try them as prices have come down. I got mine for just under £60.
My only criticism, like with the poster above, is that the E string is a bit weak sounding, I might put my spiro E back on, but I want to give it a week or so to settle down.
as for arco, I only play a little bit of arco as a practise technique, but they feel easier to bow than spiros, more fundamental.