Should I use ProMass for the web or buy my own copy of ProMass

This depends on your needs. If you have a lot of samples or are running samples by LC/MS and would prefer to automate these analyses, you should get the desktop version of ProMass.

If you only need to occasionally deconvolute individual ESI mass spectra, ProMass for the Web may be able to satisfy your needs. ProMass for the Web is ideal for a group (e.g. a University research group) to share an account. There is no limit to the number of computers or users that can use a ProMass for the Web account at a time. The low-cost, easy-to-cancel subscription model provides a much lower financial barrier than buying a copy of ProMass software outright for those needing only occasional deconvolution processing.