Cushcore does what it claims and does it well.
But, there are some negatives to keep in mind.
For those watching their bike and swing weight, Cushcore is a detriment. The weight penalty is one of the biggest drawbacks to this insert.
Evaluate your needs and decide if all these performance gains are worth the extra weight.
If you want some performance improvement without the weight and have trail/ XC rims, consider Cushcore XC.
Cost is a consideration as well, as is trail side maintenance.
Although it has not happened yet, I have heard trail side repairs can be difficult/ not possible because it is so hard to break the bead.
On the other hand, I have friends that have ridden out on the tire insert after blowing the tire off or getting a puncture. I purchased the bead dropper tool, which is supposed to help break the bead. I will report when I use it in action.
Bottom line: for the right rider, Cushcore is a game changer.
It made a huge difference on my hardtail and I will absolutely not go without it in my rear wheel.