Please read the forums for information regarding this question. There are many posts about experiences with these interlocks. Many of them recent experiences and some with even positive results (pun intended).
There is a search function too.
I was scared too when I was looking into what provider to use but my choice was smartstart and it worked just fine for me. The key is to get as much information as possible about it all. Then you will feel more comfortable not only with your choice but with the whole situation. Get info about what to do if you blow fails, false positives, skip a rolling re-test, etc…… Plus, can you remove the head in the cold months, which really helps start it up in the winter time I can vouch for. Also, who to contact at the company or installation center should the unit fail and all that. Learn what BAC delivers a fail, warn and pass for your state.
You can get all that info in these forums and calling each provider and simply asking them questions.