I mainline Swan2s. I've had 1 Swan1 in Eco1, 3 Swan2s in Eco1, and 1 Swan2 in BT Soft.
The BT Soft is the same texture to the fingertips as a really beat up Eco1, but with less rigidity than an Eco1 out of the box. Eco1 starts off smoother and stiffer, and beats into a more velvety texture with some floppiness. BT starts off velvety with just a touch of floppiness, and beats into a slightly more velvety texture and a bit more flop than the Eco1.
Beat in, the 2 plastics are really similar, but brand new feel quite different. Thats why I like using new Eco1 for driving and BT or SUPER beat Eco1 for closer putting.