In the Battlefleet book it says:

Small Weapon: Las-burners may be installed in Dorsal or Keel weapon capacity slots in ships of frigate size or smaller.

Does this mean that it can shoot 360 degrees in the Keel slot and forward, left and right in a Dorsal slot on ships of frigate size and smaller or are they still fixed in the forward only slot as most lances on those size ships…

~Cpt H.

It would specify if there were still fixed, the fact they are small and do not have limitations in where they can be mounted like normal lances suggest they dont need to be.
On the other hand i would avoid them as they do such little damage that unless you plan on playing a suicidal, close quarters combat and boarding sort of escort vessel, then they just arent worth the hassle.

I believe it can shoot 360, as the limitation is for Prow weapons being confined to a forward-firing Arc on tiny ships.

Kastka is correct though, the range and damage are not that good (although thematically fun). If you can fit the Power/Space requirement I suggest the Sunsear Laser Battery, as the real advantage of the Orion is that you can fire at people while running away, so you want something with a lot of range on it.

Turbo-Weapon Upgrade (Good Craftsmanship) applied to Pyros Melta-Battery in your Keel slot.

You now have a 360 degree battery weapon with extended range, no penalty for shooting at long range and automatic Fire critical hits (some of the best!).

I can't access the Obsidian Portal page for my old campaign at the moment to post a link but our frigate had a pair of those and mulched through anything of equal size and could stand toe to toe with bigger targets sometimes.