the subi motor has the typical advantages/disadvantages of a modern motor. it's more reliable, has more power, more fuel efficient, etc., but is difficult to user-maintain and obviously has aesthetic issues for people that are trying to be true to the classic nature of a spyder. greg seems to have gotten the bugs sorted out with the subi motor now, after having built at least a couple.
i chose somewhere in the middle and ordered a type iv motor from jake raby. more reliable, more power, and smoother than a type i, and still at least an air-cooled porsche/vw motor.