For use outside, the whether the iSine is appropriate will depend on how much of the noise around you you want to hear (and how noisy it is where you are). As some have mentioned, retaining the ability to hear what's going on around you can be desirable for safety reasons in some situations. I use the iSine at work for a similar reason; I don't want people to have to tap me on the shoulder every time they want to get my attention.
However, I would not use the iSine for cycling in traffic, because the way sound comes *through* them makes it hard to tell where sound is coming from, which is hazardous. YMMV. And on a noisy public transit commute, I don't use them b/c I know I'll end up playing them louder than is safe.
If you want isolation, look elsewhere. If you want something that's open or semi-open but are concerned about the fit and price of the iSine, nice earbuds (VE/Shozy/Yuin/Rose/etc.) would be an excellent alternative.
As folks have probably gathered from browsing this thread, iSines tend to be a lot of work compared to other earphones. Getting the fit right, getting the right tips, figuring out EQ, etc. It's all a bit much. (But worth it if a semi-open in-ear planar is what you're looking for.)