I have used them with kids, though I don't like to. Like you, I have found that you don't have quite the same feel with the Nexiva catheters as you do with a "standard" catheter. Another issue is that our "standard" catheters were 1/4 inch longer so that actually made it a little easier. The Nexiva product pretty much requires that you puncture the skin and nearly immediately also puncture the vein to ensure good placement, especially if the vein is a little deep. All of our "standard" catheters that we stock now are 2-2.5 inch length and we use those for US placed lines. Every great once in a while I'll grab one of those and use it for a regular PIV stick. I just wish they'd purchased the slightly longer Nexiva caths...I've only used the regular nexivas, I like them for EJs and patients with HIV or hepatitis. I refuse to use them on kids though, you just can't feel the same with them.
Do you find that the diffusion still flow quicker with blood or albumin?
One interesting side benefit of these is that I can rotate the needle to do a bevel-down insertion technique if I need to. I don't do that very often, but it can help obtain placement in certain situations.
Incidentally I have noticed slightly better flow rates with the Diffusic catheter when infusing more viscous fluids than with a standard catheter. The biggest "benefit" of the Diffusic is that the catheters are a bit more stable (apparently) during pressure infusion (like contrast CT) than standard catheters and they do have a slightly higher flow rate so you can use a 22g for a CTA. You still must use the same sites for CTA as with a standard catheter but when your patient has smaller veins, going 22 vs 20 can certainly improve the chance of successful placement without turning your patient into a pincushion. My default for most adult patients is an 18 or 20g, though a 22 will do if necessary.