It takes 5 Fission reactors (3.75MW) to make 1 PFR2.
PFR2 only makes 1.3MW. It also takes up 5x5 slots.
The Vanilla PFR makes 2.5MW and takes 4x4 slots.

Even if this is meant to be a Fission Reactor Mk2 (despite using the Fusion sprite), it produces either too little power, or takes too many slots, for the cost it has.

Suggested tweaks: Bump the power up to 1.5-1.75MW, halve the recipe cost (10 prod 3s, 2 portable fission reactors), reduce it to 4x4 like the regular fission reactor.
Any of these would be a good buff (all 3 would probably be too much of a buff)

Of the options, I like "reduce size" the most, as it will allow it to be used in armor earlier in the game. I also wasn't happy with the efficiency of this reactor, although it's still better than the previous version.

Makes sense to me. Smaller is the better choice, and prevents having to reorganize your grid.