i use it, its great for realms with only medium crown authority... If you can control your characters libido, there's really no problem. Have kids until you get an heir with the traits you want.
The main downside is that your older siblings will usually get claims on your titles when you inherit, but crushing pretenders shouldn't be too big of a deal for anyone that's played this game for 30 or more hours. Another downside is that ultimogeniture heirs often inherit while underage, meaning regency, which we all know is ridiculously boring. BUT on the plus side of that coin, by the time you come of age you will more than likely have a long reign bonus with your vassals.
The main downside is that your older siblings will usually get claims on your titles when you inherit, but crushing pretenders shouldn't be too big of a deal for anyone that's played this game for 30 or more hours. Another downside is that ultimogeniture heirs often inherit while underage, meaning regency, which we all know is ridiculously boring. BUT on the plus side of that coin, by the time you come of age you will more than likely have a long reign bonus with your vassals.