Very bad. The 10 neons are okay, but the tiger barbs are a big problem. They are feisty fish and WILL be fin-nippers in that small space. The guppies will be a prime target. Tiger barbs need a minimum of a 30 gallon tank and a school of at least 10 tiger barbs. Guppies also do best with groups of three or more; if you want a mix of males and females you need two females to every male.
The 10 neons and few guppies will fill up the upper parts of the tank. If you want another fish in there look at substrate fish like cories.