I almost always use a tarp, sometimes with a bivy... and have used the Equinox bivy about two dozen times. I have the older version that lacks a hood, but I believe the fabric is the same.
The advantages of a good tarp, for me, outweigh the slight loss of weather protection and longer setup times. For one, a large (at least 8x10) tarp offers alot of space for one or two people, and the fact that there is no floor means all of that space can be used to sort wet gear, cook, or dig out for seats/sleeping platforms in snow. This is great. It is why I love tarps in the rain- set them up, get inside with no worries of soaking your floor.
A well setup large tarp (I use a Golite Cave 2 mostly) negates the need for a fully waterproof bivy, or any at all if you have a good shell on your bag. Thus, the DWR top of the Equinox is suitable. It will handle a bit of moisture, but it's real suitability is in how it breathes. If I used a smaller tarp, I'd use an Epic or Event bivy for better water protection.
Even though the Equinox breathes well, I always get a layer of frost between the bivy and my bag when sleeping out below freezing- always. Of course, this occurs for me regardless of what bivy I use.
The silnylon floor of the bivy is very slippery and you can end up sliding around alot if you do not do something to mitigate this issue... the zipper is a non-locking type that allows you to simply yank on the fabric and it will open.
However, this setup lacks bug protection, and is not suitable for above treeline. I have a few netting options (A16 bug bivy, another bug bivy from Equinox, bivies with netting) but all are a pain to use and restricting. If bugs are a serious concern- seriously consider something like a tarptent.