I bought this product through a readers digest promo two years ago. It was the SB-104 model and it worked really well!
I used it in the apartment building we lived in when I saw a roach. There were units around me that had serious roach problems and I only ever saw one or two a month. Still gross, but better than infestation.
When we moved into a house last year we had a problem with mice. The house was really old, had lots of holes and places for rodents to get in (which is why we don't live there anymore!!) but it worked there as well. I had two of them. One plugged in the basement and one in the kitchen. We saw maybe one mouse after that, but they certainly didn't multiply. And considering all the holes, that's pretty good!
I don't know about spiders (or any other bugs), but we were never really bothered by them.