Thank you both for your replies.
After buying the Seydel Favorite, I did consider taking my learning seriously and bought a Special 20 as per many online recommendations - I had heard that it was easier to bend than other models. Unfortunately, some of the holes squealed so bad, neighbourhood dogs came round to complain. I'll probably come back to it at some point, but for now bending can wait. I'm quite happy to keep a harp in my pocket wherever I go (the Seydel pouches are great for that) and pull it out for a quick 'n' simple fun tune to lift my spirits. The people at the bus stop don't seem to mind either!
Interestingly, when I did attempt to learn to bend on the LLF, you get a pretty neat didgeridoo-like sound. More like tonal changes than a true bend, but a cool sound nonetheless.
Today I re-watched the Thunderbird promotional videos again. I'm sometimes sceptical of these as they're not necessarily impartial, but there was a point brought up that I missed the first time round:
The reeds are made of a thicker material, as opposed to having extra metal soldered on. The Favorite does indeed have extra metal on the end of the lowest reeds. It then occurred to me that there must be some impact on playability due to the physics of inertia and momentum on reeds which are heavier on one end...
The upshot of this is that I became convinced enough to order a Thunderbird.
Over the past few months I've been spending way too much money on different harps, but at least I've taken care to choose models and keys that ensure my existing ones don't become obsolete.
I'll post some thoughts on the TBird when I receive it!