Boric acid works the same as Borax/MA for adding borates to pool water BUT boric acid is much, much easier to work with and well worth any cost differential. Borax is a strong(ish) base and will raise pH dramatically upon addition. This is why you must add muriatic acid to compensate. Eventually you balance the two but, in the process you create both borate ions in water and lots of excess salt. Boric acid, by contrast, is a weak acid and even with the full 50ppm addition (~40+ lbs for a typical pool volume), the pH will only go down by around 0.3 units. Boric acid also dissolves very rapidly in water and will not cause calcium scale or water cloudiness as borax will.
You can do the calculations on Pool Math but, roughly speaking, adding the full measure of borates using boric acid lowers the pH by 0.3 units. Adding 1/10 th the amount of borax needed to get to 50ppm raises the pH by nearly 0.9 units and thus requires MA to knock it back down. So, you can add all of the boric acid at once OR you can add the borax in 10 batches with MA additions in between.
By far, the boric acid method is a lot easier...