They are not very well known in North America but are quite well established in the UK, AU and NZ.
I've spoken with Scott (the founder) several times and he seemed like a very nice man who cared about the industry.
One of the interesting things about his service is that (I believe) you can use it to send without being a member and paying the related membership fees. It seemed like a good option for florists that don't do a lot of sending and are not quite ready to commit to a membership.
We've used Petals for faster, more affordable sending to Europe and Australia. Service has been good, communication is direct with the filling florist, once the order is placed. No complaints on my end.
Petals have very helpfull staff at there call center have done numerous orders for them and have always been paid very promptly, same day every month, the founder scott is always availabe at the end of a phone if you have any questions or call free phone 0800-0329-878