ALS, Ferret50, Ligimec and Safety Harbor are the ones I would recommend if you plan on buying one. STAY AWAY from BOHICA now Valley Ordinance Works, they have a horrible track record in safety and customer service.
As for the lower, don't worry about any issues as all it does is provide the fire control, no stress is put on it at all. It will not wear it out, break it...
If you have any questions about how they shoot, the ALS and Ferret 50 hold world records for 1000 yard accuracy. They will put a Barrett to shame all day and twice on Sunday, best part is they can be bought with NO FFL middle man as all they are is a part.
What you need to decide is what you want to do with it, plink or competition. If you want to shoot all ammo types get a standard chamber, if you want to shoot competition then get a match chamber. If you get a match chamber you'll need to prep all you brass as the tight chamber usually won't allow standard brass neck sizes to chamber.