Has any one ever used one ? are they effective?

TBH the amount that are sold second hand, I would think they are useless

Yes I've got one, had it for years, and only used it a handful of times, however, each time it was used was successful.  Used it twice on a bitch who had very erratic seasons, and each time got a good mating and a lovely litter, and loaned it to a friend (different breed) who had also been a problem getting into whelp, she had a litter too.  They are not a quick and easy test - you need to use it for quite a while before the bitch comes into season, to establish your bitches normal pattern, record the results carefully, and then plot the results from the start of season to find the "peaks" in the readings (can't remember the whole thing, it was quite a few years ago last time it was out of the box).

I guess if I had another bitch who was hard to get in whelp I would use it again. Went to a fertility talk by Keith Shea shortly after getting it, and he was very scathing about them, but that may jsut have been a competitors point of view.

I have also been using one and my bitch was receptive on the day it said to go.... But I am on day 16 from mating now so still awaiting if she is pregnant or not! i do think she has taken as her nipples seem a little more pink and her floss hasn't gone back yet which it normally would have done by now :-)

If its any help I used ovulation pads, they were a bit fidly at first but after a couple of times they were fine. This was the first time I used them and my girl was ready on both days and I got a litter of 5.

I used the ovulation pads along with the saliva test. Both showed that she would ovulate Sun or Mon so took her to stud today. Mated with 20 min tie with no problem at all. Would really reccomend in particular the saliva testing as it is easy and inexpensive . Only the cost of a small kids microscope

I've got one and it has been accurate on a bitch that was ready on day 6. She had a big litter from one mating on that day. I would always use it from the start of a season. Some people us it to test bitches in season that aren't going to be mated just to get an idea of any patterns.

With one bitch a swab said "go" but the machine didn't indicate the same and we had to wait another couple of days before the bitch would stand for the dog. Like Gwen I told one fertility specialist about it and she didn't rate them either.

I told one fertility specialist about it and she didn't rate them either
It wouldn't be in their interest if we all did it ourselves would it?  :)