I'm not a fan of retractable leashes. I own one and would never buy another. Personally, I find them very uncomfortable to hold.
But my biggest issue with them, is the PEOPLE at the end of the leash

It seems like 99.9% of the people that use them are inconsiderate idiots! They give their dog way too much freedom so they are a nuisance to others.
I LOVE being able to take ZoE places with me and want the experience to be a pleasant one for myself...as well as for others that don't particularly like dogs. I don't want her being with me being a problem for anyone so attitudes change and people want to ban dogs from places/events I like to go to. The flexi-leash folks have a tendency to ruin this. Too many times I've seen dogs over-extended and not within the owner's control, so they annoy other people. It's especially a pain on our local walking trails where bikes, rollerblades, joggers, etc., share the path. I've seen people topple trying to avoid a dog.