Having had a good experience with the MK320, I decided to buy the MK520 for use with my laptop.

I just received it today and my first impressions are, compared to the MK320:
1) It's just a little larger (dimensions are about 17 3/4" L x 7 2/5" D) than the MK320 (dimensions are about (17 1/2" L x 7 1/10" D), however, whereas the MK320 is rounded at the top edge, this is more square. 
2) It has a built in wrist rest which is about 2" deep if you measure from the bottom of the space bar.
3) The keys are chiclet style whereas the MK320 is the typical keyboard keys.
4) Keys have a rougher texture than MK320 (not sure if I like this).
5) Caps lock key has a smaller raised rectangle positioned from the top left which leaves a space to the bottom and right of the key.
6) Num Lock key also has raised rectangle but this occupies the entire width of the key but stops short of the bottom.
7) Alternate functions are highlighted in orange, whereas the MK320 is in blue.
8) the Insert, Home, Page up, Page down, Delete, and End keys are arranged in two rows with three columns, this allows for the arrow keys to all be arranged in the space between the letter and numerical keypad - unlike the MK320. 
9) The F1 - F4 keys serve as hot keys provided you touch the Fn button - the MK320 has dedicated hot keys for this.
10) There is a battery level indicator function (Fn + F12 key).
11) On Top left there are buttons for rewind, play/pause and forward (these are on the right in the MK320).  On top right there are buttons for volume control and the on/off switch which has a green led.
12) Above the numeric keypad are keys for web surfing - back, forwards, favourites, and the calculator.  Unlike the MK320, there ins't an additional backspace key.
13) The mouse on the MK520 (mouse is m310) doesn't have an on LED light, unlike the mouse on the MK320.
14) On/off switch for mouse is on the underside - same as for MK320.

The usb receiver is tiny, it projects less than an inch when plugged in - approximately 1/4 inch and it can be stored in the battery compartment for the mouse.  Its a unifying receiver which means you can use other Logitech wireless products that have the unifying feature with just one receiver.

I am typing this review with the MK520 keyboard and haven't hit a wrong key yet, despite using it for the first time.  The multimedia keyboard that this replaces was smaller and had slightly off key placements which I couldn't get accustomed to, despite using it for over a year.

The battery life for this supposed to be 3 years for the keyboard (AA) and 1 year for the mouse (AA).  Will update when I need to change batteries.

The unit also comes with an extender cable for the usb receiver.

As with the MK320, there is no software, and no LED indicator lights for Caps and Num lock.

UPDATE
Having used it for a week now, I find the mouse doesn't seem to be as good as the one that came with the MK320.  There are times when the mouse doesn't seem to respond as quickly (a bit of lag) as it does on the MK320, found that out playing a time-based game. Not sure if this is a result of the unifying receiver.  BTW the MK320 keyboard doesn't appear to be detected by the MK520 receiver, probably because the MK320 keyboard isn't part of the unifying group.

Recommended: Yes

Amount Paid (US$): 29.90