These are getting used more and more in PVP pickup battles. Especially becoming quite frequent in MID era fleet battles.
In some cases you might see more than one. In most cases the fleet without the mauler is at a serious disadvantage, unless the mauler fleet does not provide adequate protection to the mauler ship or the mauler fleet orders up too high a station speed and doesn’t allow the mauler ship to recharge its primary weapon. The real advantage occurs when the "mauler fleet" slows down and starts to starcastle around the mauler, protecting it's weak flanks. The may do this after an initial "run" at your fleet at higher speeds meant to do some inital damage on one of your ships.
Mauler ships do not come with a robust array of defensive and offensive subsystems like many CL's, CA's or BCH's (the BIG exception is the Lyran STL) but if used correctly they can be fairly dominant at their BPV in the same way the ROM WB+ can dominate it's respective BPV. The difference is that a mauler cannot be weaseled away, cannot be hit and run, can apply damage to its opponent instantly from range and looks like it charges a LOT faster than an R torp. In other words once the mauler ship gets a lock on you there is very little in the way of counter tactics available except perhaps a near perfectly timed HET.
I was told by one player that the narrow firing arc of the Mauler put it in the category of a "skilled" weapon to use. My experience in some practice runs using the mauler was whatever skill this takes is fairly minimal in SFC. If you slow down between speed 10 - 15 and put your helm on "auto follow" you should have little problem maintaining a lock on your opponent in most circumstances. I practiced this with a fairly skilled Klingon pilot who atempted to sabre dance in and noticed I never once lost lock. I even had time to hit the fridge and pop a Budweiser.
One tactic that seemed to work briefly was a zig HET zag maneuver. My Klingon would come in at an angle (actually an angled arc) and HEt at range 11 or 12 to the opposite angle slicing in under range 8.9 to deliver a phaser disr double salvo. Then he would scoot out into mid range again. He was able to break a shield and do some damage to my hull, but not my number one shield. In return I was able to HET and counter strike for far more damage to his number 4 shield, a bad shield to lose for a Klingon.
The real skill in operating the mauler seems to derive from power management after firing your first salvo. I notice a lot of Mauler pilots are not using reinforcements to their front shield and I found out myself that the Mauler wont charge if you try to reinforce that shield, or any shield for that matter. Without consistent use of reinforcements the Mauler ship appears to be susceptible to PPD, Hellbore, Proxy and Enveloping Plasma attacks (R and S torp only due to range limitations on G torps). It should be noted that R, S and PPD ships are pretty rare or non existent (PPD) except in pirates at some of the low BPV's these ships can play at.
Anyway as an advisory to those playing online PVP I would say this is one ship that probably plays with retrictions in SFB and probably should in "real time" as well. If you know you are going up against one you better start thinking of getting one yourself or, as an alternative, using fighters.