I can't tell you how they would work, unfortunately. I decided early on that I liked the pen a little longer, so I have never used the tubes that come with it.
The "short spring" issue has been around on many roller ball "kits". Years ago, the manufacturers said it was "personal preference" and the spring could easily be stretched.
Just not an answer I particularly like, so I have purchased replacement springs in the past and will do so again.
When we have them, we will offer them as an option when buying from us. We like to offer you as many options as possible, so you can customize the pen to YOUR customers" likes.
If you use these "opportunities" correctly, you can distinguish yourself from the other pen-turners at a show by asking the prospect, "Do you like the feel of that, or would you prefer a "softer" writing feel? You don't need to use it to go through carbon copies or "carbonless" forms, do you?"
Makes you sound smart!!!