I have a Stratus II, which I've had for about 1 1/2 years. Its only downside compared to XM is that it can't provide service on the ground. However, for that, if your iPad has cell coverage, you can still get the current weather on the ground at any ordinary airport. Obviously, unless the back country strip you're at also has good cell coverage (I suspect some do), you won't get weather on the ground, which you could get with XM.
The upside of any ADS-B In receiver is that using it is free of any charges. Buy the product and use it. The downside is the same as with XM, that the weather is delayed. How much of a delay is visible on the iPad screen, typically varying from 5 minutes to just under 20 minutes.
The Stratus II only works with Foreflight and an iPad, but it works seamlessly. I have mine plugged into power, so it stays charged whenever the avionics are turned on. It also has an AHRS, so it provides an electronic AI through the Stratus Horizon app, which in my experience is right on. I can use that on my iPad, but more often I use it on my iPhone as a backup, so that I can use the full screen on the Mini for charts and weather.
When I renew my FF subscription, I plan to spring for the new synthetic vision option, to try it out. How useful it will be is questionable until I try it.
Cary