Hi rgrebby
LRMogrify is donationware - meaning if you use it and it works for your workflow, you then donate an amount according to what you think it is worth to you... very fair I feel. I donated £25 as far as I can remember.
As for web export - sorry, I don't use that function in LR, so I can't really comment. I do know though that if you use 'file>any of the export functions' you can add up to 3 lines of text (any size and transparency) as well as an image based graphic, anywhere on your photograph. Lots of customisable options etc...