We have had a Barefoot Nevada for ages, one of the first i think.
They did slip a bit, but it does depend on A) how round your horse is and

How level you sit!
The newer model has a gullet, so this should sort this out. i also recommend buying the model with the dressage girth straps rather than a cinch. The pressure is taken more evenly at both sides, and use a short dressage girth so that your fastening the saddle lower down, making it more stable. invest in the correct pad, and you have an inexpensive saddle that works well until you youngster is matured and ready for the saddle that hopefully fits him the rest of his life!
I like ours, and it fits anything to boot!There is some snobbery around about saddles, but for value for money and versatility I would buy one. I have had ours 6 years, had no trouble with it.