1) The attack function does not work, they can still blow each other up.
2) you must ground fire them to make them work= noob unfriendly as it is counter-intuitive and not something you would immediately think of= noobs stop using them= excludes noobs like me from playing so well as cybran
3) It takes multiple clicks every time you want to try using them=less time to micro everything else=major detractor from your peformance in the overall conflict.
Example; you move to attack, spend 30 secs (maybe slightly less) setting up your beetles to attack the right location then oh wait, his units are here need to turn around and pull back= all that time wasted= much less damage from kiting your hoplites effectively with losses possibly incured as a direct result. This kind of scenario is regularly played out (without beetles), as players creep forward an back to try and get an advantage.
Solutions:
1)Get rid of fire beetle
2)Increase damage to 10000 and remove ground fire so that when one does work theres cause for celebration
3)Fix the attack function
4)Remove direct attack function and make ground attack default
Ideally 3, 4 if not and 2 if neither of these because I can't stand something only working with a maximum of micro, even auroras/hoplites/mercies work to an extent if you just point them in the right direction.