What's so good about a chronos chess clock? That's a really expensive clock so it must have something really good about it.
I've not used them, but people report that they physically stand up well to heavy blitz use.
I have read the manuals of all the major digital clocks, and the Chronos clocks seem to be the second most flexible in number of timing modes and variations they support.
For delay modes, they seem to have the most display options. Suppose you are playing a game with a 5 second delay, and you have 180 seconds left on your clock, so at the start of your move you have a total of 185 seconds until your flag falls. There are at least three ways that clocks display your time on your move.
1. Some clocks display the total time until flag fall. They would display in this example 185 seconds (03:05) at the start of your move, and that counts down. When you finish your move, they add back the minimum of the 5 second delay and the time you used on this move. This is how the DGT 2010 and DGT XL work.
2. Some clocks display the time, not including delay, and mark the delay by some kind of flashing indicator. These clocks would show 180 seconds at the start of your move (03:00) and would flash the delay indicator for 5 seconds before the display time starts counting down. I believe this is how the DGT North American works.
3. Some clocks display the time, not including the delay, and also display the remaining delay time. These clocks would show 180 seconds (03:00), and also would show 5, and the 5 would count down to 0, and then the 180 would start counting down. The Excalibur Game Time II works this way.
It is important to note that these are all acceptable in USCF tournaments, and are in fact mathematically equivalement as far as time keeping goes. That is, any given sequence of move times will lead to the flag falling at exactly the same time on all three kind of clocks. All that differs is how they present your time to you.
Despite being equivalent, some players have strong preferences for which they want. The Chronos clocks have support for all three.
PS: I said that the Chronos seems to be the second most flexible clock in modes supported. If you are curious, I think the most flexible is the DGT XL. It's manual mode lets you construct a time control of up to 5 periods that mixes periods of any timing method that makes sense, no matter how weird. You could have a 30 minute period, following by a 1 minute byu-yomi period, following by a 20 moves in 60 minutes with 5 second delay period, followed by a sudden death 60 minutes with a 12 second increment.
As far as I know, the Chronos does not let you go that wild (nor does any other clock I know about).
I bet they don't stay long this time. Hopefully, there will come a time soon when they will catch up and get a surplus, so that they are just plain old available all the time in all colors/button configurations.