I was able to add the hard point kit during the build process so it wasn't as bad as a retro might be. Once the hard points are installed you are done. David builds the Pod when you are ready for it as I don't think he keeps stock on these items.
I have flown several family trips with it and we really like the affordability to carry large objects that otherwise wont go in the cabin without removing seats. We have a 3 year and 1 year old so we take everything and the kitchen sink with us. The RV10 feels as if the CG is slightly lower (below) you and it becomes even more stable, or so it feels that way. Speed penalties..... no matter what I say most wont believe me, but I tested during phase 1 and only recorded a 1 - 2 knot penalty. David shows (I think) 6-8 knots penalty and I discussed this with him. He has it that way essentially because no one would believe him if he said what the real world numbers are similar to what I just did. Just remember he is offering the pod has a speed enhancement.
The pod is a work of art, you can buy it painted or straight white gel coat. There is some assemble required, wheels, lift mechanism, cables, etc. No big deal to do.
I have a Show Planes cowl so I had to modify how my engine air flow exit the cowling. The Show Planes cowl doesn't require any 'extra' vents, louvers, or doors to help it cool the engine. But with the POD sucked up close behind the cowl air flow exit it did put back pressure on the cowl and therefore drove up my temps a little. I ended up putting cowl flap just for when I have to POD attached. Otherwise no need for them if using the standard Vans cowl. I also have extensions for my exhaust pipes to allow the exhaust to flow furhter out and away from the underside of the pod/belly of the aircraft since in my case at a high angle of attach the exhaust went straight for the wing root. You know what that means.... All is good now with the extensions as I only use them with the pod. Again I am not aware of anyone else needing them with the standard stock cowl.
I think other peoples experiences will vary on what is required and what is not, each build is different so don't read this post the wrong way. Your mileage may vary.
*** My oldest will always ask if we are going to land on the water when we put the 'boat' under the plane.