ICS Challenger review part 3 - conclusion 

Key points:
Good price considering the hop up chamber and advanced frame but total performance is limited by the slide set;
Expensive if upgrades are considered (require basically a complete upper) to make it as competitive as an upgraded TM that costs as much as the base gun;
No as versatile as a TM for advanced builders.
Buy if:
You enjoy recoil (will be a very heavy slide with red dot on);
You don't plan to upgrade (lower isn't TM compatible enough and is good enough/you would be looking at a complete new upper if you want significant performance change);
You plan to use it for secondary;
Don't buy if:
You plan to use it as a base gun for upgrades (TM and KJW are cheaper and better);