Hi Eukleides,
Yes, the ride quality of the 8" model is a bit better than the 6". However, the folded size of the 8" is not as small as the 6" and the folded package is not as neat as the 6", too.
Here are my answers:
1. The newer saddle is already more comfortable than the old saddle which was used on older model of A-bike and A-bike Plus.
http://www.abikecentral.com/forum/viewtopic.php?f=2&t=2080Of course, you can replace the stock saddle with a standard one if you can find a seat post with correct diameter or you have to install an adaptor on your A-bike.
http://www.abikecentral.com/forum/viewtopic.php?f=2&t=20402. Here are the world-wide distributors of the A-bike.
http://www.a-bike.net/Best regards,
Amuro