The biggest trouble for them is the question of how to play them.
They don't have a codex, nor have they so we are left having to proxy them.
Then is how do they look? We have some descriptions of them and a few Blanche pictures but no models so they will be an entirely scratch built force which i think is slightly beyond the average gamer.
I think I have only seen this as Imperial Guard, indeed a lovely force is found here [URL]http://www.lounge.belloflostsouls.net/showthread.php?6462-Adeptus-Mechanicus-Imperial-Guard-a-WIP-blog[/URL]
Oh found this which is a Grey Knights count-as going through the henchman route
[URL]http://www.lounge.belloflostsouls.net/showthread.php?15830-Adeptus-Mechanicus[/URL]
And miteyheroes has a nice little blog about his Ad-Mech [URL]http://admech.blogspot.co.uk/[/URL] which is worth a read through as he has some neat conversions.
A space marine list as ad-mech
[URL]http://www.warseer.com/forums/showthread.php?176971-Jimbobjeffs-Skitarii-cohort[/URL]