Well I'm not sure that my judgement is necessary here as many seem to say the same thing..
I did a placement with Beneteau when I was studying Yacht and Small Craft Design, and it made me swear never to buy a glassfibre hulled yacht. I have since been on two Beneteaus in calm environments, and both have had a significant quality-related failure.
It is not the flex directly that is the issue, but the fact that flex causes delighful things like
1. Deck and hull moldings to seperate at sea
2. Rudders and steering to fail (flex around the mounts/gudgeons)
3. Starring, cracking and then leaking through the moldings around the mast foot
These boats are purely for coastal work. I'm not necessarily recommending 'Crab Crushers', but I will say that with second hand 'modern' boats, you gets whats you pay for. There's a very good reason why Beneteaus are cheap!