It's personal preference at the end of the day but I just couldn't bring myself to buy a brand new boat. Same with a car. For 12.5k you are getting a brand new 4.7m rib with a 40hp engine. Don't get me wrong, I'm sure it's a fantastic boat (and it might suit your needs perfectly) in which case ignore me.
For me I like buying a quality, looked after second hand boat and getting much more boat for my money.
In fact there was a really nice 6.5(ish) metre Osprey that just went over here for 10k, 150hp engine with low hours, all brand new electronics, lovely condition. I would have had it if I had the money. If I had paid more for a brand new "cheaper" RIB I would be disappointed sat next to that at the boat park.
Like I said though it's personal choice, there is obviously no warranty second hand and you don't always know exactly what you're getting.
I'm probably not helping in the slightest!