I've got an old one that I batch dried with for years.  It worked very well except for the babysitting required to get many bushels through it.  About ten years ago I got Agri Steel out of Lyle Mn to help me automate it with Kahler controls.  Now with the addition of a wet bin, I can dry nearly 1,000 bushels per hour taking out 5 points at a fraction of the cost of a new continuous flow dryer.  My Top Dry was already connected to several 48' storage bins so I already had a lot of the infrastructure in place.  I think even if I was starting from scratch, I would consider using the Top Dry again.  I've got no complaints.