As to buying Matt - it also sounds like you had a lot of responses to just that specific question as well.
What are you planning to do with your horse? If your goal is high-level eventing or something really strenuous - well someone pointed out that can be difficult as the horse gets older. But for most types of riding - low-level schooling, trail riding, etc - 16/17 really is not that old. So if you like Matt, then go for Matt.
However, it also does not hurt just keep an eye on what is out there and see what you find. The benefit of Matt is you have ridden him and you know what you are getting. With another horse they may seem great initially but some buyers just aren't honest, so buyer beware.