They definitely are not stiffer than Spiro orchestras, and are maybe even less stiff than Spiro weichs. But this is the thing about Animas: they are low-tension but they don't *play* like low tension strings--you can dig in and get a humongous sound from them.
It also definitely helps to crank the action up when you put them on (although it will rise naturally as the top becomes accustomed to the lower tension, or at least that's how it worked with my bass). If you have them too low, you miss out on all of the good qualities of the strings.
It took my last set about two weeks to stop stretching, and it's a freaky experience on my bass because, before the stretching occurs, the red wraps at the top of the string were hanging over the nut well into half-position. By now, they are well above the nut and everything is normal.
I must say that it may take longer to become accustomed to the strings as a player than it does for the strings to become accustomed to the bass, but the rewards are very great. I had my first set on for about two months and decided to switch back to spiros because I felt like the strings were just too "different" for me, but those spiros were only back on the bass for one day before I realized that I had entered a completely new and superior world of tone production with the Animas that the Spiros could not hope to match. The steel strings were flat and two-dimensional, the Animas were three-dimensional and round and blossoming. They went back on the bass and I haven't looked back.
As far as bowing goes, I worked hard at getting used to the Animas and thought I had made a lot of progress. Then I spent a month or so playing arco on a bass with steel orchestra strings, and when I went back to the Animas with the bow I could barely get a sound out of them...the technique required is rather different.
Lastly--anyone who puts Animas (or any Velvet strings) on their bass for an hour and then decides they don't like them (as we hear of on TB on occasion) is wasting their own time and money. These are not typical strings! It takes a long time to really evaluate them--in my case, about three months. Sure, the G string will feel ridiculously thick if you're coming from Spiro weichs, but this is not an impediment once you get used to it (in fact, from listening to recordings of myself on gigs I can say for certain that I play with much more agility and clarity on Animas than I did on Spiros, which is contrary to the first impression most of us have when trying Animas for the first time). Some people may feel like they don't have three months to give to an adjustment period (gigs and such), but this is a small amount of time compared with a lifetime as a bassist.