Custom abutments for dental implants are best and usually more expensive to fabricate it what I use 90% of the time, rather than a ready made abutment.
it basically means that your dentist is taking the care to provide you with an abutment custom made for you, rather than one "out of the box". This should provide you with the best possible orientation of the crown which should in turn, if the lab does an ideal job, make for the best esthetics.
Custom abutement are used on a regular basis when restoring implants. It is an excellent choice when needed.