Emap
I've used one for a couple of years now.
For:
Cheap, reasonable screen, slim, not too heavy on batteries, takes cartridges and MetroGuide, inexpensive RAM mount, can attach external antenna (if using in a car or boat)
Against:
Not waterproof, no autorouting, poor backlight, needs special power lead (as it only accepts 3v supply), smaller screen than 176
Overall, it's a good low-cost solution. Pay more and get the 176C, pay lots more, get the SP III. Pays your money and takes your choice.