The ergonomics on the SM/BA compared to the 883 are great. You won't feel as cramped up as on the 883, and Triumphs don't have that annoying vibration that Sportys have. The range is greater, too.
There are plenty of aftermarket parts for Triumphs, but not nearly as many as there are for Harleys. I have NEVER had any problems with
www.newspeedmaster.com and as far as I am aware neither have the vast majority of the other folks. I would not hesitate to buy anything at all from Newspeedmaster.