The Laserjet Pro 400 is living up to the published information and to my expectations. The results are crisp and sharp. Colour rendition is fine, including photos (although it wasn't purchased with picture printing in mind). Although I haven't yet tried anywhere near the full range of media the printer claims to supports, the results with those that I have are all excellent.
I have a Linux based network and set up as a wireless network printer was straightforward. At the time of writing the M451dw is a recently released model so it was necessary to install the latest version of hplip from the HP website first, but in due course this should appear in normal distros.
Service from Printerland was excellent with rapid delivery as advertised and personal follow up to confirm receipt and satisfaction.