There are several parts to a trigger job on any 1911. The hammer and sear are important but only two of the parts. The trigger has to fit tight and still ride smooth in its track. The disconnector needs to be polished where it touches the trigger/sear and be smooth in its hole. A lot of the final effort necessary to pull the trigger is resistance to the sear (3-finger) spring.
There are two parts in smoothing the sear, the primary angle and the secondary or relief angle. The primary angle must be precise all the way across and all the various fixtures enable you to do that more precisely and repeatedly. All of the tools help you with the primary angle because that is the critical one that touches the sear. Realize that there will be only about 0.020” of contact between the hammer and sear.
The relief angle lets the sear get closer to the hammer so a smaller length of hammer hooks can still work. It is not as critical for either angle or length. The flat should be almost as wide as the primary angle and here is where the adjustment pins and a good magnifier really helps (especially with old eyes). Only some of the tools help with this because it is relatively easy to do with just a stone and the sear in your hand. Both the Marvel’s and the Ron Powers Series I both do. The Ed Brown and the Brownells do not.
The hammer needs the hooks shortened to about 0.020” This can be done in the Ron Powers Series I or in a bench vice. Both require that you put a feeler gage blade on the hammer and cut the hooks down to match. Then you need to polish the face of the hooks, while maintaining exactly 90° to the face of the hammer. You can do that in a Ron Powers Series II fixture or on a lathe tool with some lapping compound.
All these things can be done by hand without any fixtures, but how many sears do you have to ruin before you have paid for the fixture? The Ron Powers Series I will also do most other sears with other adapters.
Also if you do any work on any of these parts, when you take it to the range, load only one round and shoot it about 5 time or so to ensure you did everything correctly.
Have fun