You got me curious enough to check it out. Ad or not, that is one of most incredible sites I've seen with deep resources that are very valuable. I learned a lot in the 20 minutes there. The 'interstitial' is just that -- a plea for donations to support the writer and hosting for an ad-free (it's ad-free for everyone, not just donors), high-quality resource. I had to read the page 3 times before I picked up on the instruction to input the root URL into the address bar, instead of being linked there. Haven't looked at the code, but is he just looking at referrers and dynamically routing based on being on his "graylist"?

If I find myself there more, I'd be inclined to send him something.

As to its effects, I think he'd prefer to drive off any and every reader who is offended by the ask. They are just costing him bandwidth with zero chance of any return. Maybe they share it with someone who ends up donating, but people who actually donate are much more inclined to be good sources of referrals to other people who may donate.

As to whether it equates to posting a link to an ad or promotion, I really don't think it crosses the line. This isn't one of those informercial sites that lead you on for an eternity without ever providing anything of substance. Instead this is just an interstitial on steroids meant to drive off undesirable traffic. It's 1000 times better than annoying ads and/or anti-blocking measures, imo.

There could be valuable content there, but I will newer know that because I followed a link in comment, but all I got is an ad asking me to pay for something.

Wow. I wonder if that page actually has the intended overall effect. I've never seen this site before, but the actual content seems useful and (perhaps unsurprisingly) well presented. That said, hijacking me to another page to condescendingly nag me (and not even including a link back to the content I was originally linked to) really puts me off. I really think that the kind of people the author claims to want money from would be better reached by simply making it easy to donate.

Works for me.

I guess because I have been to the site before, Matthew has just an irrational disdain for HN readers.

So the poster probably didn't even know about this redirection.