i used A1 SD Bench just for curiosity's sake. i get about 55MB/s write on the card and 90MB/s write on internal storage.
the read speeds are very different (71MB/s card and 297MB/s internal) but for the amount of data being accessed at a time, the difference is negligible. i'd rather be able to actually utilize my sd card vs have it sit there with 50MB worth of images while my internal storage sits at less than 6GB free.
as for "messing up an $800 device" this method will do nothing of the sort. it's not a hack of the system, it is a built in method to utilize a method that is still in the OS, but has had the user facing (GUI based) option removed. but the Command line still exists.