Well, if you're a person that goes "...I should'a...." then go for the VP2+. But, if to save some money the most useful (in my opinion) of the two sensors, and also the least expensive by a couple of hundred $$$, is the solar sensor. But, as 92merc stated, it's much cheaper to buy the VP2+ rather than to later purchase the two sensors. I'm in the same boat as 92merc...I bought the sensors later, too.
But, I've been happy with them.
ETA... After thinking about it for a minute, I really could have done without the UV sensor.