Spartite is an excellent solution which serves both as mastboot and mast collar. For difficult to fit mast collars, like our CS 36T, where the halyard exit boxes are only an inch above the partners, Spartite is the only good solution. For most boats, there are a variety of other, cheaper solutions to a mast boot that may get the job done. Two common ones are a self-sealing tape and a pre-formed boot that you cut to fit.
You need to figure out what will work for you, I tried three different solutions for our mast boot before I spent the money on Spartite, which has worked very well.
Certified...in several regards...