I bought it long ago and I'm very happy with it for my needs - a very inexpensive simple Photoshop replacement. If it didn't exist, I would be in a bad place.
I'm also quite smitten with Pixelmator: it's full-featured, robust, cheap, fast & native! For my purposes, I honestly prefer it to the much clunkier and much more expensive Photoshop.
Have you tried using Pixelmator actions in Automator to replicate pixel-precise cropping? See http://imgur.com/nDTcxvS I recently processed hundreds of screenshots this way and it worked well.
I still wish they'd add one feature that I sometimes need and feel very helpless without: http://choorucode.com/2010/02/08/irfanview-replicate-crop-on...
Trying to draw a pixel-precise selection with mouse when you have an exact number in mind (that would so easy to type) is extremely frustrating.