2 things: 1. Base level Mek are 51, unlocked at level 91, with blueprints for higher levels obtained through the normal way (titans or OSDs). 2. They starve without fuel, and need element to sustain themselves.
Do not fight a level 290 corrupt wyvern with a level 51 primitive Mek. Let's just say they self destruct. 40 element plus other mats just exploded. Thank God for glider suite, that shit blasts you straight into the air when it explodes. Still died wyvern got me on foot. Fml.
*WARNING* Keep Element on meks at all times! As long as your mek is out you must have element on it otherwise it will despawn/die. 1 Element per day it is out seems to be enough. Fist bump this to make it known. I've lost 2 meks with no trace even in tribe log because of this.
At high levels they can output extremely high damage, especially with the sidearm it comes with doing extra damage to Corrupted. You can even fit these things in the caves, however it feels as though they have no damage resistance and can take a lot of damage VERY quickly.
When creating the Mega Mel for Alpha King Titan you must defeat Beta King Titan First to get the attachment to make a mega mek. A mega mek requires 4 meks to combine as one. You can use the base level 51 meks to create the Mega Mek. Once the fight is over you lose all 4 meks that you have used. So advised to use 4 level 51s as stated. Fist bump to bring to top so nobody wastes mats making high leveled meks for the fight.