How many units sold total? Only a rough number!
roughly few thousands

I had hoped many more would have been sold by now given 141,614 subscribers to /r/Bitcoin and 393,788 accounts in bitcointalk. Plus the hundreds of millions spent on ASIC preorders.
I think many of the "early adopters" are already competant with computer security. Trezors are critical for the mainstream adopters though who have no clue how to secure a computer. When that happens I think the sales will pick up.