Gefen DVI detective is fine - and has been around for a few years. Its relatively easy to program - just a button push and it copies the device EDID. Thats it...
Price point is about £84 (cheaper if one purchases in bulk...) Lots of resellers.

The Kramer VA1DVI is the same as the DVI detective, made under licence from Gefen by Kramer.

The Pharos Parot is better:
http://www.dviparrot.com/
It can also be easily programmed with just a button push, which copies the device EDID.
However, it is also user programmable via USB using the 'Parrot training' software - allowing custom resolutions to be programmed which cant easily be done with the other two products.
Price point is higher: aprox £176.00 each (cheaper if one purchases in bulk...)
...but it is a more flexible product - not that expensive
if TBM are quoting £298 - you are being ripped off.!

TIPS:
You can use a programmed parrot to program a DVI detective...
- Program the parrot as required with custom resolution
- connect a Gefen or Kramer DVI detective
- capture the EDID with the DVI detective from the Parrot.

So if you already own DVI detectives, it can be easer to program them with custom resolutions using a Pharos Parrot.

You can also use any of the above to prevent a mac from enabling HDCP when not required, if using a system which includes both HDCP and non-HDCP compliant equipment. (ie DVI over cat5 or DVI fibres)


Do let me know if you need more info

Simon