Have been reading here about the different ways to buy maps from different inmates. Downloads, SD Card, CD. The reason I bought the CD is because they are the only ones that have lifetime updates available. You can't do that with the SD card or Download. From what I understand.
As far as TOPO maps. I have yet to find a trail that is on a TOPO that is not on my CNNT. I don't see the need for the topo personally. The CNNT maps are that good...