The Pfaff 2140 had a bad bobbin winding system. Pfaff did issue a fix, but the Sidewinder does a better job. The 2144 does not have this problem. (both have vertical bobbins)
The Sidewinder is still handy. I always forget to wind extra bobbins for almost all sewing, so I use the Sidewinder rather than disrupt the threading - although you can wind those Pfaffs through the needle. The Sidewinder takes almost every bobbin, I have a collection of old metal ones that I use for the serger. You can wind specialty threads for a small job with the loopers, or one bobbin will do a Tshirt on the needle side.