First of all, the rule is not flexible. If you're using EZSlide, you're breaking the rule. Doesn't matter if you think you're "applying it properly" or not.
The question then becomes whether your personal ethic allows you to break a rule and still bowl. That's up for you decide.
It becomes up for me to decide for you when I catch you doing it. I have turned people in for it before -- although, only the ones who just absolutely dumped the stuff everywhere.
People who use it minimally, or people who use ashes, usually know how to do it well enough that it doesn't affect me. Like others have said, though, it must be a mental thing for some of you, because there are many ways to get around ever having to use it -- slide socks, proper wire brush techniques, teflon pads, the slate Dexter sliding sole, etc.
The times I've turned someone in, it's been because they were affecting my approach, or others' approaches. My wife bowls despite herniated discs in her back, and she nearly went arse-over-teakettle on night despite having virtually no slide, because of a woman I used to bowl against who would literally powder her sole every shot to the point she created a cloud of talc around her. Her own team captain couldn't make her stop, so the league stopped her. She got mad, but she complied.
Basically, my view is this: Use it at your own peril. I'm not going to turn you in because I can't beat your score, but if you put EZSlide out there, and it gets on my slide sole and I bust arse because of it, I hope you like forfeits, because you're going to have one.
Jess