Good question. What I measured and what I haven't:
- Compatibility renderer: yes, on desktop. The demo project actually ships set to Compatibility. I ran the full demo and every effect under Compatibility (OpenGL 3.3), Mobile and Forward+ on Godot 4.7.2: both shaders (flash, dissolve) compile, no errors or warnings in the log.
- Cost (Compatibility, desktop, whole-frame time, i5-13450HX + RTX 4050 laptop, effects looping non-stop): 1 explosion ~1.2 ms, 5 ~1.8 ms, 10 ~2-4 ms, 30 ~4-4.5 ms; 30 small impacts ~2 ms. Forward+/Mobile were 0.3-1.3 ms faster in the heavy cases; most of the cost is the GDScript painting, which is the same in every renderer. An earlier run of the same benchmark gave higher numbers (10 explosions 6-9 ms, 30 about 17 ms), so treat these as a range, not a promise.
- Web export: not tested yet. I haven't exported it or run it in a browser, so I have no web numbers. The code uses no threads, no file access and no OS calls, and the shaders are plain canvas_item shaders, so I don't expect a blocker, but GDScript running in WebAssembly will be slower than the desktop numbers above, and I can't say by how much until I measure it.
- One known detail: the dissolve noise pattern differs slightly between GPUs (it uses a sin-based hash). It still works, it just won't be pixel-identical across GPUs.
The free sample (impact, sparks, ring, flash) is the same code as the full pack, so you can try it in your own web build before buying.