I can second what Astrid and Sheree said about "Choice". They have a great section where all baby products are reviewed and tested. It can really put your mind at ease.

I wasn't a fan of the three wheelers either initially as I had also heard they were not stable. We had a four wheel layback pram but due to various problems with it, we had to return it to the manufacturer and get a refund. I used the "Choice" website to help me choose a new pram.

As Astrid said, some of the models are great but some have problems and it is also true that any stroller has the potential to be unstable if it is overloaded or used incorrectly.