Looks like I accidentally found my exact right starting level for spinning, by simply not having an earlier week than this left on my phone. I don't think I'll be too much in a hurry to push on from here. Took a bit of time to figure out how to set up the parameters (and the effort level I initially chose was impossible to budge). Because it's a new set of muscles that are emphasised, I was surprised at how close I was to not being able to walk when I got off at the end.
So what's nice about spinning? This afternoon I zoned out at one point watching the buildup to a good try by Griquas (underdogs) against the Bulls. Something like that can probably make you more completely forget that you're flogging your legs to death than the real world does, out there on the roads that were made for running.
The machine also gives you your pulse rate. Looks like my resting pulse rate is falling nicely, for starters (below 80 in the "walks"), and I know that if I'm doing 140 I'm up near the upper limit of what I can sustain for any length of time. 120 is a nice level of effort (and when I started this c25k, I'm estimating that 120 would have been where it was starting to get difficult). I pushed a bit, but somewhere in the low 150's was enough for me. Anyone pushing up above that is really giving it stick. It's nice to have an instantaneous "effort meter" like this.
It's also better than a treadmill when it comes to adjustabilty of pace. You pace yourself; the machine doesn't pace you.
What's not so great about spinning? The worst is that your cooling system doesn't work properly without the wind you create by moving through the air. If I ever set up something like this at home, I'll have a big fan blowing on me. Drips of sweat mean you're running hotter than you should. They're meant to be evaporating to cool you. I also don't like the wide stance. I keep drifting in toward the middle, and losing the pedals or getting snagged. Give me a bicycle, rather.
On a balance, it's an adequate way of staying fit if there's nothing better (like running) available, so I'd better stick to it. Exercise is just going to have to be work that one has to do, instead of a small adventure somewhere out there, at least for now.