I recently used long-handled secateurs at somebody else's house, and they were a dream to use. I think the extra leverage provided by the long handles helped. My host had no idea of the make as they were a gift.
The secateurs had two curved handles covered in red plastic. They were short enough to operate one-handed, but long enough that they were too big for me to close one-handed if they were fully open. The blades were curved, and slightly longer than my ordinary little secateurs.
I couldn't see anything remotely similar in our local garden centre.
Any ideas?