The Pro has 4K front resolution instead of 2K, so twice the detail.
The Pro comes with a free CPL, while it is an extra cost item on the Plus.
The Pro has. a 9% wider front image field of view, 112 degrees vs 102 degrees horizontal field of view, so it can see significantly more at the sides.
The Pro can see 33% further, 20 meters vs 15 meters for reading a UK license plate, when looking straight ahead.
And the old A229 Duo only has a Sony Starvis 1 image sensor instead of a Sony Starvis 2 image sensor which is a big upgrade, especially at night when using HDR, and also has a wider angle lens, close to that of the Pro, combined with 2K resolution, so can only see about 13 meters for reading a UK license plate. Also, the old A229 Duo is missing voice control, and has slower Wi-Fi.
The A229 Plus has the option of a 3rd channel for the interior, not available on the A229 Duo.
If you are upgrading from the A229 Duo to the A229 Plus, then it is worth noting that the cables are different, using USB connections instead of coax connections for the remote cameras, so the old front to back cable will need replacing. The power cable is compatible, and I think they can use the same hardwire kit. Not certain about the hardwire kit for the Pro, it is possible when upgrading that some of the older hardwire kits are not powerful enough.