I was using Spiro Mittels and now Eva Weich. On my bass Eva feels softer and slightly looser than Spiro, which is a dream because Mittels after 3 years still feels stiff. Ah, sounds louder, all strings, E is floor-shaking.
And Evas are thicker, which gives you more stability for fingering. Eva sounds darker, old-school, but has the perfect and enough bright, even in the lows and specially on the highs. And bows easy, has a shhhhh smoking sound...lovely.
The only concern is when playing amplified, Eva has less mids so if you need to cut through in a loud situation, you will have to add mids in the EQ.