PRIME does seem expensive, compared to other brands. That is until you read the recommended dosage levels. PRIME is far more concentrated than many of its cheaper counterparts.
And SAFE, the powdered form of PRIME, as mentioned, is crazy crazy concentrated. Value for money blows everything out of the water with this product.
The only downside is that it is extremely concentrated and measuring it out can be very tricky because the amounts are only small, especially if you only have small tanks. SAFE primarily benefits hobbyists with huge set ups but that's not to say others can't use it too. Some hobbyists buy tiny special measuring spoons to achieve the right dosage levels.