Just got back from my first run in the Inov-8 Trailroc 150s - they have them in stock at Rogue Fitness. Only ran 3.25 miles since it was supposed to be an off day, but couldn't resist a run in new shoes!
The 150s are definitely ultraminimal, no midsole at all. There is a removable insole with a finished footbed underneath - with the insole removed there is only a thin layer of cloth and the lugged rubber outsole between your foot and the ground. The outsole is similar to that of the Trailroc 235 (which I also have), so protection is decent, but you will feel rocks, ice chunks etc. As with the 235, traction was great. About half of my run today was on rough ice and packed snow, and never had a slippage issue.
My main concern with these shoes is the upper. It's made of a plasticy mesh like in the New Balance MT00, and it creases across the forefoot when it flexes. It actually makes a noticeable sound when it does this. I worry that repeated flexing may lead to tearing, time will tell on that. On the plus side, it lacks the harder overlays on the sides of the upper of the 235 that have caused tearing as reported in the Trailroc 235 thread
One more note of significance - the 150 is narrower than the 235, my guess is it helps to save weight (150 is 5.9oz in size 10 US). Measuring the sole across the lug row behind the "meta-flex" groove, the 150 is about 6mm narrower. However, without the insole there was plenty of room for me in the 150 - wonder if it is higher volume?
Here are a few photos - the yellow sole on the second photo is the 235, and you can tell that it's a bit wider: