I've been trying the seat strap, neck strap and balance hangar thing when I play lately, as well. I'm not real crazy about the feeling that I'm "wearing" my bassoon, but it does seem to help the left hand. Even better, I can let go of the bassoon completely to throw up both my hands in disgust when practicing, and the bassoon continues to float safely in front of me. Nice.
What sort of neck/shoulder strap do you use? I saw one that puts the hook at your side instead of the center, but I wasn't sure if that was good for standing only, or for sitting, as well. I'd be interested to know if there's a "right" way of doing that.
I wear my bassoon. I've been doing it since I had a nasty bout with tendonitis about ten years ago. It is the only way I can get through even half an hour of playing without pain, and I never could have done it before I had a balance hanger. I use a BG shoulder strap with two hooks that I sling sideways across my chest - over head with one arm through.
Just recently though, I picked up an IDRS journal and saw an article with a different twist. The author still uses a seat strap and a neck strap, but the neck strap is looped through the back of a chair on the right side and hooked onto a regular, basic neck strap hook on the bassoon. Weight of the instrument is taken by the dual straps and your right thigh. It works beautifully and keeps the weight almost completely off of the left hand, more so than my usual balance hanger and neck strap method. The only two downsides are 1) you must have a chair with a slotted back, and 2) range of emotive movement is severely limited.