I like the looks of Traxxion's Bitubo they sound like a great product. I guess I just need to do some shoping and research on this. I would like something I can adjust for solo riding or pasenger on board.
Van
I've got the Bitubo shocks on the rear of my 05 SEEG and the Progressive 440s on the rear of the SERG. Those are probably the bookends of levels of improvement we're likely to consider with Bitubos being about the best and the 440s being the entry level of improvement gain. Others falling in between.
There's many others out there "less" than the 440s that don't do much more than the OE pieces do. But there's no reason to go there for such limited gain anyway.
The Bitubos definitely offer a better ride than the Progressives. But, of course, they cost more. The Progressives will bottom out and will do so with some significant report. The Bitubos can hardly ever be forces that far. Both are significant improvements over stock. Make the bikes ride much much better and with much improved handling.
The stock Showas just aren't that great of a shock. The systems nearly all leak a little so you're too often topping off the air pressure. The shocks are weak and don't handle that well. I honestly can't think of a single reason to spend a dime accessorizing the stock shocks in any way when that same money could replace the shocks and actually make the bikes more comfortable to ride and better handling.