I don't use mapping chips, I just put a big enough microSD card in it that I can download all the detailed MapSource data for about half the U.S. at once and still have room for routes, tracks, etc. This is the 3rd eTrex Vista I've had and love them. I started with the original Vista, then a Vista C, and now the Vista Cx. I considered the 76CSx when I bought this one, but its overall size is much larger, and the screen is only very slightly larger when the total area is measured (i.e., the difference in screen size looks greater than it actually is). The Vista has no capability to connect an external antenna but so far I haven't needed to.
That accessory bin is OK, but not great. It did loosen and slide down over the winter, but Sunday I was able to stick it back up where it is in the picture and it held with a relatively heavy hand held VHF in it on a VERY rough lake. The suction cups on it are just OK - not great.
The mount is from RAM. They've had a great reputation for device mounts for years, and they have a solution for just about everything made. They aren't what I consider cheap, but the quality is unquestionable. Part of the secret is their modular design approach. That mount is actually two products. One is the suction cup & swivel, the other is the actual holder for the GPS. They have many, many different types of mounts - suction cup mounts, handlebar mounts, dash mounts, floor mounts for laptops, etc. - and holders for tons of devices. I didn't buy it direct, I think I got the part numbers from RAM's site and then bought the parts from Amazon IIRC (it was over the winter).
http://www.ram-mount.com/