For anyone who's interested; thought I'd just post-up my experience of testing out the Pod...
Test kit; 40D + 100-400 - mostly fully extended at 400mm... In-car in a safari park in the UK...
Net overall impression; pretty-good. Clearly has plusses & minuses like any other piece of kit. I've yet to find the perfect solution to all eventualities
Major plus over a beanbag;
- Fixed to the lens; so when you move the kit from one side of the car to the other; the Pod moves with you and you can settle the lens immediately without needing to re-seat a beanbag.
Major downside;
- Fixed to the lens; so when you want to hand-hold the lens, it's added weight that you need to take into account.
I didn't find the levelling or portrait use an issue. Levelling just needed a jiggle about - just as you would on a beanbag; while using in portrait mode just required slackening off the tripod collar. I did find though that keeping the Pod on the collar in portrait mode worked well when bracing against the car door jam... not something easily done with a beanbag.
In short - I will be taking both the Pod and a beanbag with me in just three weeks time - yippee!