Mechanical dimensions are a tiny big larger than 3.5x3.5 but the solder pad remains the same, should be within the margin of tolerance for the centering of most lights
Hopefully they are available in consistent good tints, and with a lot (!) less tint shift with higher currents. Also the beam quality in optics is hopefully much better. The SST-40 is not good in this regard.
Luminus emitters are - apart from the warm white 95 CRI variants which are really superior - simply not as good as other LEDs…