A little heatsink is plenty for an SSD. But only when it actually intercepts some airflow. Just sticking more heatsinks onto parts doesn't do much when they're not getting any air.
hehe, finally something I can comment about with experience.
I run two Evo 960s in raid - which means you don't get individual SMART info like temps. So I did a backup and wipe to break the raid and test it. I showed an idle temp on one drive of 42ish and another was 38C. But I couldn't figure out which was which. If you've watched some videos you may recall the heat sinks actually increased temps. I put it all back together and tried the temp probe on the motherboard and the fan controller board. Couldn't get those to stick on the nvmes. Finally I broke down and bought an infrared thermometer. That did the trick, I found the top nvme was the low temp - so the heat sink does work.
With extended use - CrystalDiskMark - I saw the un-sinked lower drive get up to 50C maybe 52. I believe this is well below throttle but I wasn't stopping there. So I bought an EKWB nvme sink. It's a serious pain to install on the bottom slot and I ended up cutting back some of the padding on the drive but I did make it fit. This means I could only test the heat sink fins with my thermometer but they did show a nice drop. I haven't run the whole break raid and test but based on the thermometer the bottom nvme is coming in about 3C below the top now (Maxed at about 44C). So while I could have been happy without the additional heatsink, I'm not concerned at all after adding one. They do work and for $12 it's not a bad investment for peace of mind.
(Edit: my case config has a 280 rad in push/pull in the front of the case with nothing restricting air flow to the MB)