Hi JohnJP,
The pros are that it's a great television with the inbuilt surround decoder so if this is your first BV there is no need for any external AV receivers. Also the Avant features WISA so will connect to any WISA speakers or other speakers attached to wireless receiver 1's.
I bought the Toshiba BR player that you mention and i used to play CD's on it attached to the BV and that would be enabled in the multiform with other devices. I did use it as a BR player but i started to buy a few 4K BR discs and the toshiba is a non 4K BR, so i put it in a box and connected an Xbox to it and set it up as 8bit 4K
You can also buy the clamper system from STB brackets if you wanted to attach any peripherals on the back. If you go for the BR player then STB also make the bracket for that too. Let me know if you want any pictures.
The cons are that the video engine could go or if it has been replaced on the one you're looking at it should be fine. The issue from what i understand is that it overheats as the cooling in the back of the Avant could have been better. It happened to mine and at that point i was wondering if i don't bother with a new BV or spend the money to change the board. I'm glad I changed the board. Even though it was expensive, everytime i use the Avant, i like it.
There was a software update, i think there was only like 3 or something, and 1 of them changed the HDMIs so that nearly all of them are 4K
There was a Mk2 later on that featured android (which i have on the BV14), but I don't use the OS, i just use the my buttons on the remote for the sources I use, and the android version is so old and didn't feature netflix. the Mk2 had improved wireless too but if you're running ethernet it doesn't matter. The Mk2 also got rid of the quick access HDMI on top too i think. Also with Android there are no updates with that platform as soon as they changed to it, they left it behind.