When I spring for a Mek, I like to give him the Forcefield, the Toolkit, and plenty of Grot Assistants. These can be handy. I played a 400-pt Combat Patrol where my army had one of these badboyz... plus 3 Killer Kans and also all the boyz I could get. I marched up the field with the Kanz in front and the Mek right behind. The Forcefield was big enough to cover my whole army. My opponent was practically crying when every time he immobilized a Killer Kan I would just fix it! Although it doesn't always work, this time it did for me - the Kanz eventually busted through his battle-lines, killing all, and the Boyz arrived next to clean up the remaining resistance.
The Mek cost a lot, but if you can find ways to use him like this, it pays. 100 points to improve the saves for a whole unit of Boyz can be a good investment. Not quite sure how he could be used for Freeks, tho. Ideas?