What will keep the razor slits open? Usually when you cut a slit in a relatively soft tube, the slits will close up and greatly restrict any flow through them. Saw cuts work because they remove material from the slits, but razors don't remove any material. UGF's do work, but not very well for planted tanks. Reversing the flow through them (RFUG) so the debris is trapped under the sand seem to work better, but still not that great. And, you would still need wider slits or holes to get good flow.
Also, larger particles work their way to the surface in substrates, so the pea gravel at the bottom will eventually be on top of the sand.