Unfortunately none of that is quite true.

Free
Yes, for the Thomson demo (which is ancient). There still remains, to the best of my knowledge, asubstantial lciencin fee on a per unit basis to manufacturers of codes and decoders, frees which are substantially (50-100%) higher than for mp3.

It encodes your mp3s at 64kb/s but retains the quality of a 128 recording
Nope. The quality is equivalent to somewhere between 96kb/s and 128kb/s. And then only if you encode form the highest possibl;WAV, preferable the original.

less than half the space of the original mp3.
Er, depends. It takes up more space than a normal 64Kb/s MP3 (since in essence it IS a 64Kb/s MP3 with an additional stream carrying the higher frequencies)

It'll play on anything that will or can play an mp3 file
Indeed. On the other hand it'll only playback the 64Kb/s part and totally ignore the PRO part if your player is not an MP3Pro player. Which almost nothing is these days*, and certainly not the players on the n800, n810 and n900 or, indeed, the n9. So if you've been hearing a difference ... well, it is, I'm afraid, all in your mind.

In other words all you are doing is turning your 128Kb/s mp3 into a 64Kb/s mp3. Only with a file size that will be slightly larger than a genuine 64kb/s mp3.

Obviously they were going the right direction in their r&d to entice or worry a corp like dolby to absorb them into a division of their company.
Entice, rather than worry, I'd argue. The spectral band replication (SBR) technique originally developed for mp3pro made its way in HE-AAC.

An irony might be that HE-AAC v2 is also commonly known as enhanced AAC Plus, or eAAC+, which is the M4A format that Nokia PC Suite used to like converting your music files to before downloading to your phone ...

*If you bother looking at the MP3Pro website that you yourself link, you'll notice that all the devices and software mentioned are at least 10 years old. They suggest that they'll update the site when they hear anything new. It was last updated in 2005 ...