The Echo I is really a great shelter. Very well made, durable, well designed, and cool looking.
Ultimately it comes down to size. The Echo I tarp is just small for my liking. If pitched low to shed more wind, there is little headroom and shoulder room. One can make the argument that you really don't need to pitch it low with the solid 1/2 walls on the inner, and that's true. But with the tarp alone, it can get tight, especially when you add in the front pole.
I must note that my tarp comes in much smaller than spec'd on HMG's website. I don't know if they sized up a bit on the Echo I since I got mine, but the front width on mine is only 6' when stretched out flat, and is spec'd at 7'. The rear width is something like 6-8" smaller than spec as well. Length is about right.
The Stratiform is much bigger. Two people can sit side by side in the front, and depending on pitch, one can sit upright nearly halfway back towards the foot end. It reminds me of an elongated Trailstar, especially since I have the optional rear beak installed. It seems very livable.
Downsides to the Stratiform: larger= more weight (but not much), larger footprint, and may have more deflection on the side panels.
This isn't a fabulous comparison shot, but you get some idea of size difference. The Echo beak is attached in this shot.
I'd like to note that I have not had the shelters up side by side yet, and have not spent a night in the Stratiform. For every other aspect but size, the Echo is still a really fabulous setup.