If you don't have the money in your budget but you desperately need (or want) the player you are about to sign, then the option for Monthly Installments is great to have. It's easy to work out the amount that goes out, just divide the amount of money by the amount of months and you will know how much of your budget is going out each month on your signing.
'Is it better?' isn't really a question that makes sense when it comes to Monthly Installments, sometimes it's necessary (as you don't have the transfer budget to sign a player without it), and sometimes it is not. But if you already have the money in your budget to sign your desired player, don't opt for monthly installments, as there is little point to this (Unless you want to sign multiple players).