Agree about the NH600, but only up to a point. Outside the UK (where you can easily get an NH700) the NH600 has much better availability. If you look at the service manuals for NH600,NH700(incl. NHF800) and NH900 you will see they all share a common mechanism, so, features aside, you're getting basically the same product.
The big trick when buying an NH600x machine is to ask the vendor how many sockets/connectors it has. I have seen (and/or seen pictures of) many variations. My own 600D purchased here in N.America has no line in, and NO 3V POWER CONNECTOR (the yellow hole that takes the yellow-tipped jack from Sony and other suitable adaptors). This might be a big deal for you, or it might not. The rationale is that the device doesn't really need power at all as long as it can draw some from USB, during downloading.
The NH600, on the other hand, has a nice power input, and a WHITE socket for line-in (analogue/optical) as well as the usual USB socket and remote-connector. Don't let weird pictures put you off, my strong belief is that they ALL have the right socket for the "standard" Sony remote control.
Note one big difference of the NH600 from the higher numbered (in this case bigger number = better) models - it cannnot recharge the NiMH battery when you press the stop button. Even if there's a yellow connector. However this shouldn't stop you as Energizer NiHM chargers and AA batteries are so cheap that there is no reason for anyone to buy anything expensive from Sony.
It seems that many of the NH600's were made for outside the USA. Mine came from Oz, and of course any model from down under, or Europe will (if supplied at all) have a charger that needs 230V. Again not a big deal but don't be surprised if you get some funny shaped plug you can't do anything with.
The jog dial is not as solid as it might be, and a little smaller for big fingers, but don't let that put you off. The 3-line screen is an excellent feature that older models never had. This is a nice machine, and perfectly adequate as backup to a microphone-capable RH910.