Pea gravel is awesome, you just have to "seal it" so your finer fills don't infiltrate, reducing their volume and causing shifting. That's why it's not used as often anymore, and they've come a long way in understanding compaction so they often require ca6 or sand compacted to a certain density. A fly ash slurry is a form of flowable, works great. In Indiana, they had an outfit that basically added a single bag of cement to a whole truck of sand, making a flowable that was easily to dig later. It set up and all, but there wasn't enough cement to make it hard. They basically did this so they could very rapidly fill streets without a compactor at all. Around here it's made right, so it's got more cement and hardens accordingly. I literally flipped out the first time i saw that they were gonna pour right against the pipe, because if it was the flowable that i was used to you would never be able to dig it up safely. Only the paving crews had to have a compactor, and they just needed a small plate one for doing asphalt. Doing that with flowable would make it an easy job compared to worrying about compaction.
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