I haven’t tried the strawberry butter, but I hear it’s excellent.
What I like about the powders (which is actually freeze dried fruit that I powdered with my food processor) is that, because there is no liquid with them, you can add what amounts to much more actual fruit to your buttercream. Also, they have no sugar, so they don’t affect the sweetness (except that, depending upon your taste, you might need to add more sugar to offset the fruit’s tartness—I didn’t). Finally, because you can add so much, you get great color without using any food coloring. Also, they don’t thin the consistency, if that holds any importance. You could use it to color frosting for a rose without using food coloring (if the flavor would blend), and still have a very thick mousseline to pipe, for example.
That said, there’s no reason you can’t use the strawberry butters and then, if you wish it had more strawberry ‘punch’ (and maybe it’s perfect as is), you can add freeze dried fruit powder—so you can use them together, as well.
FWIW, I’ve found both the Crispy Fruit brand and Today’s Farm brands to be really good. The bulk ones from Nutsonline.com are not quite as good. The Juststrawberries brand (that also makes blueberries, etc.) is very good, but their packaging somehow allows humidity in so it doesn’t keep them super-crisp for a long time (unless they’ve changed it), and the crisper they are, the easier they powder. The ‘pouches’ seem to be the best packaging for long-term crispiness, and the plastic containers the worst.
Another nice thing about the butters is you get a nice “uncooked” fruit flavor (maybe same with butters, etc.) and there’s lots of flavors, depending on the brand. I’ve used strawberry and banana, but I plan to also use Asian Pear, apricot and peach in buttercreams. Here’s a link to my post where I used the banana: http://www.realbakingwithrose.com/index_ee.php/forums/viewthread/3364/
They can be a little expensive. I’ve found it costs about $9 of freeze-dried fruit to flavor 6 cups of mousseline (it takes about 1/2 ounce fruit per per cup of mousseline). I don’t know how that compares with the butters.
I’ve thought about adding some strawberry to the cake itself, but I’m going to pass on that this time, because I’ve never made this particular “cake bread” (as my friend’s son calls it) before, and I want to really get to taste it.