I've never used restrainer, but since I have a lot of outdated Galerie graded paper I've made notes from AA's "The Print" for future use. Here's what my notes say:
1. Prepare a 1% solution:
Dissolve 10g BTZ in 900cc of water, then add water to make one liter.
[B&H info says use water at 125F or higher due to difficulty in dissolving]
2. You might begin with 25cc of 1% BTZ per liter of stock Dektol. Use only enough to clear paper fog. Adding 50cc causes a noticeable shift toward blue. Adding 100cc will reduce paper speed by roughly 2/3-stop. Image contrast may also be increased somewhat (more so than KBr).
Potassium Bromide (KBr):
1. Prepare as a 10% solution:
Dissolve 100g KBr in 900cc of water, then add water to make one liter.
2. You might begin with 50cc of 10% KBr per liter of stock developer present in the working solution.
Check on the effect of the bromide and add more as needed for the desired effect.
Bromide sometimes adds a slightly greenish tone to the image, which can be overcome in most cases by selenium toning. With modern papers, bromide produces a warmer image. Paper speed will be reduced, requiring longer exposures – possibly longer emergence time as well, requiring lower than normal development factors.