I haven't seen many reviews for Patagonia's approach shoes that comment on their quality as an approach shoe. I've seen a couple but, for the most part, the comments are about their comfort as a hiking shoe.

Does anyone have any experience using the Finn's, Huckleberry's, or Karakoram's on class 4/low-grade 5 approaches? I'm trying to get a sense for how sticky the rubber is and how good the toe design is for edging.

The trouble with these shoes as a climbing shoe is also their strength as an approach shoe: they're really light, and so much nicer to carry up the route, and comfy for approaches. However, their lightness comes at the cost of climbing well. Because they're not board-lasted, they fold in cracks like a taco, and the rubber on the sole is almost like foam, so they suck for edging and smearing. Ledgy fourth- and fifth-class is ok, but I take them off for anything technical. In comparison to, say, LaSportiva's B5 or the Mountain Master, they are more comfortable but poor climbers.

Of all of them the Karkorams would be your best bet. Complaints about the Huckleberry's and Finn's approach snuff are probably what brought about the Karakorams, which are newer. Karakoram's use stickier Vibram Approach rubber, and a more durable construction. I have used my Finns for some scrambling and light hiking (and I like them for everything but their durability), but I would definitely go to the Karakorams for Class 4 and low grade 5-- if you fit them well.