Pros: Fast and stable - this is a good instructional boat for smaller people.
Cons: Not a playboat. Displacement hull can feel "mushy"
The Dagger Piedra is a great boat for the right person. It was designed as a smaller version of the much larger Dagger Animas. If you've ever paddled the Animas, you might wonder why Dagger would spend any more time developing such an awful design. To me the Animas paddles worse than a 20 ton garbage scow. It is long, heavy, and has a flat rear deck that cannot be used to carve turns easily (like the RPM for instance). You might be suprised to find, then, that I actually liked the Animas' little cousin the Piedra. I found that the Piedra paddles somewhat similarly to the RPM, the best selling whitewater kayak of all time. There are a few significant differences, however which depending on what you're looking for can make it better or worse for you.
Like the RPM, the Piedra has the older style displacement hull which gives the boat a large amount of secondary stability. I feel that this is important for beginners (it certainly was for me when I was learning to roll and stay upright in class II rapids). Most current boat designs have a flat or "planing" hull. These are great for surfing and tricks, but can be difficult to learn to roll with and can be more unpredictable in whitewater. The Piedra is roughly the same length as the RPM, but is a bit more narrow and has a slightly raised (instead of flat like the RPM) stern. What this means is that volume of the boat is less asymmetric than the RPM. This more even volume distribution and rounder stern practically eliminates one of the main features (or faults depending on your point of view) of the RPM, which is its tendency to "stern squirt" both intentionally and unintentionally. This makes it a better boat for testing your limits in whitewater than the RPM be it as an absolute beginner, or challenging class III, IV, or even class V rapids. I have paddled class V with a guy who prefers a Piedra because of its relative speed and for its forgivable nature.
The boat is big enough for an average size adult male, but small enough that it is still pretty easy to control. For smaller people (who it was actually designed for) it may be feel a little more cumbersome, but most women I've talked to still find it small enough to paddle without feeling overwhelmed.
This is not a playboat. Few if any tricks will be possible in this boat, but it will front surf fairly well - especially on larger, flatter waves that newer, shorter boats will be unable to surf due to their low hull speed. On smaller, steeper waves, the length of this boat will make surfing more of a challenge.
This is a medium sized, fairly forgiving, medium volume boat. It is relatively fast by todays standards. The displacement hull means that it will be fairly forgiving, but it does not have many edges for fine and quick boat control by more experienced paddlers. The medium rocker and relatively even volume symmetry mean that the boat will have few suprises in store for the beginner, but will allow it to front surf reasonably well. I owned a Dagger Piedra for a relatively short time. I sold it not because it wasn't a good boat, but rather because my boating style didn't fit the Piedra. I have come to prefer to paddle a boat with a hard chine, and felt that I needed more of an edge than this boat offered.
I think the Piedra is great as an instructional boat for (small to medium sized) people on their first few paddling trips. For fairly hesitant beginners, it may make a decent first boat - but all but the least aggressive will outgrow it fairly quickly. This boat may also make a decent alternative to a Creekboat for the class V paddler who generally paddles larger volume rivers and wants a boat with less volume.