It's close with models like VPM also but for no-stop diving I'm ok with a Haldanian approximation of no-stop limits. I just start my "safety stop" a little deeper.
Exact doesn't matter to me. Pick up 4 or 5 different tables and notice the wide difference in NDL's.
Also when doing these comparisons notice what effect a minor change in depth has on the calculated NDL. The table or computer you use will make more of a difference than an inprecise estimate of profile depth. Even if you take the "NDL" as something that really exists it won't matter if you're not riding the edge in the first place. If I'm anywhere near something I view as a limit I'll do some minimum decompression (call it a safety stop if you want).
As far as I'm concerned good dive habits like slow ascents (especially near the surface), time spent shallow after time spent deep, and added conservativism for things like cold, hard work (during or after the dive) or multiple dives over multiple days is where my margin comes from not from precise calculations in an inexact model.