I just picked up the 42 recently on a trade, knowing next to nothing about these rifles until after I got it and did some research. I think mine has a 27" barrel, chambered in 300wm.
I was surprised to find how comfortable it was considering the previous owner had tweaked it for his preferences. I could literally get right on top of it and fall asleep. The cheek rest is peaked, rather than the rounded ones I'm used to (see Cadex Dual Strike and XLR Carbon chassis), but doesn't cause any discomfort when resting or shooting. The buttstock is adjustable for LOP and comb, however you will require parts swaps (for the spacers that best fit you) and it is not tool less adjustments.
For rails, I've scanned a lot of photos online and it seems that the go-to rail is the Near Mfg one, which is made in either 25 or 45 moa. I think Spuhr makes rings that go straight onto the Sako dovetail, so if you get that, you pay a little extra but you won't need to add a pic rail.
My rifle came with a brake, not sure what brand, but there's one on EE (equipment exchange on CGN) right now that seems like a pretty good price. Coretac makes a bunch or you can get the factor TRG one.
My rifle also came with the BT adapter for Atlas bipods. I ended up throwing an Atlas bipod on there, but I hear the factory Sako bipod is quite nice as well, and allows the system to pivot closer to the bore axis. Pricy as *uck, I think they run about $700-800?
Other accessories are pricy as well, like the $3000 folding stock. Mags run over $200 a pop.
Working the action on the TRG introduced me to a whole new world of finely crafted firearms. I can't get over how smooth it is and I'm going to say it's arguably the best I have experienced so far.
The trigger is an adjustable two stage and breaks like glass at a Bat Mitzvah. I can't wait to test her out.