Nice recent write-up about thread conditioners by Suzy Quilts - appears the benefits are greater with natural threads (i.e. cotton) vs synthetic (polyester) which is why some opinions may vary. I spent a few hours hand sewing last evening with Aurifil 50wt and Thread Magic - worked wonderful! No tangles, No fraying, No resistance through layers of fabric. I think I might also try the Sew Fine conditioner as I've seen it recommended by several quilters that I follow.
Ultimate Guide to Thread Conditioners