Firkos I suspect has had a form over function trim job.
No Marc......I bought the Boyd and Stellings swingarm on my Maico in the early 90's as a shop soiled but NOS item. It'd never been on a bike and it's exactly as it came from the factory...gussetless.
The swingarm on the TM400 has a little bit of extra gusseting but not to the degree of the one on Trade Me.
Note also the lack of gussets on the Yamaha in GMC's magazine post. As far as form over function, most long time vintage racers will know that my old Maico's been through a pretty severe race career with Laurie Alderton, Per Klitland, Pelle Granquist, Kevin Flood, Daryl Lewis and fat old me racing it with that swingarm fitted. I can't say that it's remained perfectly straight in that time, I had to 'untweak' it on the press once but it wasn't bent to the point that the bike was unridable or that I thought it'd need a gusset.
As I wrote in an earlier post, if I ever decided that a gusset was called for I'd stitch weld a 25mm X 25mm angle section
underneath the arm with the angle positioned like
V so to allow for two butt weld surfaces and a neater appearance. The way US Sport has done it spoils the whole look of the arm and just crys out 'tacky afterthought'.