I had a friend/former mentor who proved that object pools are slower in Java once GenGC was introduced because they create pointers from the old generation to the new. He also authored the fasted XML parser of that era and previously helped me land a project everyone but us and our boss said was impossible because Java Is Too Slow, so I take him at his word.

So unless those pools are full of primitive data types, you’re going to cause more frequent full GC pauses, and longer due to all the back pointers.