does she hold the bottom well? or do you hold hers?

box anchor has held 8 of us rafted together on the pamlico river during the boat races and never let loose. Mine has always set in the lakes, rivers a little hard to get up sometimes.Mine is the large version.

Small lakes and rivers aint no test for an anchor, I could probably tie a rock to a rope and it would work good.
Try your anchor in some white caps and then lets talk.

Check out this anchor
 

I have a Digger Anchor. Works great. No issues. Just google Digger Anchors. I have the larger size.

I use a 15lb Digger Anchor, fluke style. They claim use with no chain so I tried it and works great, have bought a second. Best part is you can drop the flukes and it comes up clean, no mess on the boat. Works for us.

how does the box anchor work in silt/mud?

I will never tell...... :bunnydance::evilb:

Rubber coated fluke anchor with 5' of rubber coated chain and 200' of line. Pain in the ass to get set but holds well when set with a long scope. Typically anchor in 15-40' of water so I normally don't need all that line. Deepest I've anchored is 95' LOTO main channel and "The Quarry" at KY lake which was about 110-120' deep if I remember correctly.
I also use a 10lb rubber-coated bell anchor to set the back of the boat if needed. If helps quite a bit if the wind keeps changing.

If I had to do it again, I would buy a box anchor for my main anchor.

OK, its winter.

Large Box anchor w 150' is my primary for a 25'. Small Box can not even hold my single boat in mud. Large box can hold about 3 similar boats in the wind with mud.
Quick, low scope set is good for party lines where getting a proper scope and back down to set a Danforth is difficult.

Fortress is my backup, lock down anchor w 250'. FX-23 was my intention but picked up a FX-37 (HUGE) for the same money on ebay. Fortress is compact and light but quickly assembled.

$600-700 in ground tackle seems like Overkill until you realize the security and convenience being well anchored brings. No more setting down the drink or waking up to check if the anchor is holding. Less orchestrating the movement of a boat line because it is blowing into danger. Break downs follow Murphy's Law and occur in nasty, rough weather with no one around to help, a good anchor is a Must IMO and a backup option will keep you off the shore.

So you carry 3 oversized anchors in your 25' boat? Do you have any space left for beer?