The reason your local gunsmith uses liquid because he does not want to spend time cleaning off the paste/gel.
using paste/gel GREATLY reduces the chance of liquid dripping onto stuff you dont't want to have it drip on. I plus most of the professional gunsmiths I know use paste/gel since it is only being used for spot repair and not bluing a whole firearm. Paste/Gel cold blue is very easy to apply to small areas and let it sit so you get the most color you can. If you get liquid cold blue onto a area that already has been polished then hot blued the cold blue will ruin the polish and make it flat matte looking, or even take the finish off.
There is no cold bluing chemical that you can get super shinny without taking almost all of it off in the process. There is some formulas that can be polished a bit but not more than a satin finish.
hope that helps