I havent liked Fire Prisms until now, because they seemed too expensive for what they may do. Its 160 points for a Prism with Stones and Field... And allthough you may reroll hit-results, the possible outcomes all arent really good:
- The Prism will be destroyed / immobilized=destroyed / weapon destroyed=useless / shaken=useless at least for a turn
What the Prism really needs isnt Holofields
imo. Its something else people have to shoot instead! First thing that comes to mind is ... two other Prisms

and with naked Prisms you get pretty much 3 for 2 (3x115 vs 2x160).
Now that thats sorted out, the next natural choice is more Skimmers aka Wave Serpents. With a possible load of aspect Warriors these are definately higher on the target priority list, so you get into a win/win situation. If opponents shoot at Serpents your Prisms saved a lot of points for defensive wargear. If opponents shoot the Prisms thats even better since it means the much pricier Serpents will deliver their load.