The SH 172c is not current model--currnet number is 175.
I had the 172 and it's a great machine and I liked the size and ease of use. It also has a second slot for a user c-map chip that you can load at home with way points from First Mate or c-map PC Planner on you computer instead of loading all the way point from the key pad. You can also store routes created by storing track logs while under way.
SH has an unusual mount that limits where you can install it because of way the display head has to slide onto the mount. CHeck that out on current model at West.
THe new 175 is avaiable for around $725 (Bethel Marine Electronics for one source).
I replaced my SH with a SIMRAD CE33--it hjas a lot more features but display isnt as bright and it's a lot more complicated.
I'm going to get another SH--the 175. Great desgin and engineering.