Hollow it is the lower monkey useful torso. It is a balanced torso in energy and heat. The hp at L50 it is lower than Fractured and Rusty. A bit tricky to balance but it is ok to max if no other. Now, I see you are clicking some legends parts around like runner, solar touch, energy leg. Do not bust those parts since you do not know when can get another.
Seems you have Flaming hammer. Hmm, sure you can to advance mech if no options. If you will use Hollow remember that monkey mechs do not have resist and depend of max protector or independent resist modules and with the current vest torsos with 130-180 resist might have some issues to harm enough since I do not see any enhancement to that weapon. Ok to deal a bit against others Monkey but even against EFA or Zark with full resist will be hard too. Now, if you will orient your mech for heat ok to use since the hammer it is a good one to use generally speaking and pack a punch.
In other words, Hollow it is not the best option to use faming hammer but can be switch later on. Can be good to use frantics as example.
Some users can give a best opinion. I have use it just for testing but it is tricky to make modules to be oriented to energy or heat because it is more focus to go for phys option.
Don't know..