Hi Dubious,
I don't want to scare you at all but my experience with the bier (guanethidine) block wasn't a good one at all!!
I had a Bier Block when I was initially diagnosed with RSD, exactly 2 years ago today. My Doctor put me under general anaesthetic for the block because of my age and then injected into the nerves round my ankle bone.
When I woke up from the procedure, I found that I couldn't walk. Whenever I tried to walk, my legs would shoot out in front of me and I fell to the ground. It got so bad that I had to use a wheelchair to take me everywhere and rely on my parents to take me to the bathroom ... not very nice for a teenager!!
The complications from the block lasted over 13 months and I had to go under an intense PT program to learn how to walk again. It is actually 2 years ago today since I had the block and the complications started ... we now named Independence Day 'Lack of Independence Day' as for me, it was the day I lost all of my independence!
Of course, like everything with RSD, everyone reacts different and there is no telling how you will react. My Doctor didn't know at the time that you should never inject into an RSD limb - it was only after I had the block that my mum found an article about it.
If I were you, i'd do a lot of research into it (which I know you will) before deciding to go ahead with it. No one can force you into doing anything you don't want to - it has to be YOUR decision!!
Sorry to hear about what you are going right now!

I wish you the very best of luck with whatever you decide to do and please keep us posted!