As somebody who has had a moonbump, it's a stage prosthetic and really isn't meant for kinky uses. It's fused to a bodysuit to keep it in place, and the silicone covers the crotch gusset completely, which is obviously pretty counterintuitive to sex. The biggest problem though is its fragility. It's mostly foam with just a thin covering of silicone, so it's easy to put permanent dents and creases in it. That and the foam will, over time, pull away from the silicone layer, causing the belly to look uneven and "caved-in".
Your best bet to get a better belly at a fairer price is going to be Aliexpress. There's re-sellers on Ebay but they gouge you with the shipping.
I can personally vouch for this belly here: https://www.aliexpress.com/item/4000056016204.html
My partner and I have gotten a lot of use out of it. It's solid silicone and is held in place by strong-ass velcro that wraps around the back and leaves the crotch exposed. It's much more durable, but also significantly heavier. We love the weight just for the immersion factor, but just something to keep in mind. The outie is also way cuter.
Our favorite is the 7900g, listed on there as "8-10months twins". It's the largest size they currently manufacture, and it is *huge*. The 4500g "5-7months twins" is quite a bit smaller if that's a concern for you. The silicone is also different between the two, with the 7900g being firmer, and the 4500g softer.
Let me know if you have any other questions.