Just downloaded this add-on today. Tested it out in many different ways and it realy works great! It saves me hell of a lot of time!
The only little confusing thing at the start is that one can only apply shrinking 'after' pressing the Send button. So you can add like 10 pictures of 5Mb each as an attachment, press the Send button and only then you are offered to choose in which size you want the pics to be send. Any size is possible, also the original if one might sometimes wish. And it realy shrinkes it from 50MB to something between 1 and 5MB, depending on your choice.
Because I hope the developer will keep up the developement with upcoming versions of TB, I supported with a small donation. Hope others will contribute a bit too, so we will be able to enjoy this add-on for many more years.