If your machine came with ridged baskets and you're getting a ridgeless double basket, it's a good idea to buy a replacement portafilter spring at the same time. Ridgeless baskets require a stronger spring than ridged baskets, such as on those shipped with the Rancilio Silvia, and experience shows the basket is prone to drop out of the portafilter if the spring is not replaced. However be aware that you may have difficulty fitting ridged baskets with the stronger spring in place so don't throw away your old spring if you intend to still use ridged baskets.
Note: 1) the product you receive may differ slightly in design from the images below depend on the exact style of spring supplied to us by Synesso. 2) while the springs may be a little stiff to start with, they will generally become a bit looser over time.
The portafilter spring shipped with the Rancilio Silvia (L) compared with the Synesso unit (R); note the difference in thickness.