I have thought more about this and I think your feeling dirty and your general hesitation are due to incorrect conceptualization and your using wrong terminology.

Using wrong terminology stems from a failure to approach the issue at the right level of generality. You approach it as a sex-specific issue, which is why your language is "paying for porn", and something in this language makes you feel dirty (not clear what exactly, but clear enough that it is "paying for porn" because this is how you titled the thread). Let us approach this is a non-specific issue.

As a non-sex-specific issue, on the right level of generality, and using the right terminology, this can be described as:

"I want to use premium content on an otherwise free site". Since you yourself explained that "it will also grant me a bunch of other features for using the site,", then very clearly you want to try a premium account on an otherwise free site.

This makes it akin to using LinkedIn Premium (you get to know who viewed your profile and other such things that I am not clear about since I do not use it).

This makes it akin to being on OKC's A-list (you get to browse anonymously and other such things that I am not clear about since I do not use it).

This makes it akin to paying for extra storage on a picture hosting site that provides free storage up to a certain level of GB.

Etc.

So nothing to feel dirty about.

Your next question is whether it is discreet. Since the site per you is legit and apparently values its reputation, why would they make it not discreet? They have an interest in retaining you as a client. Theirs is not a hit-and-run deal so they would want to be discreet. No guarantees, but at least it would not make sense to them not to be discreet. Plus, what could be "not discreet" with this kind of transaction? It is not like they would send you unwrapped vibrators to your office address - there would be an entry on your credit card bill, and that is it. If you really care, you can ask them what entry it will be - most likely it would not say "fetlife" but would mention some kind of an intermediate entity with a plain name they are doing business as - you can ask. In general, our credit card bills are private to us. Bank account statements might need to be presented to third parties (say, if you are qualifying for a sliding scale), so if you are that concerned about privacy, do not use your debit card for this transaction as the charge will appear on your credit card statement. Use a credit (non debit) card instead.

Your next question is whether it is a waste of money. Again, approached generally without making it sex-specific, the best way to find out is to try. Since they are not interested in hit-and-run, they should have some sort of a short trial or a way to cancel the subscription if you do not like it. Use that option with the following precautions:

- do not use Visa/Mastercard but use AmEx/Discover because AmEx/Discover have a much better customer service and offer online dispute resolution for most (not all but most) transactions. That means that if you want to dispute a transaction, you can do it fully online - no snail mail, no calls. Much better.

- If they have a free trial option, for a month, then schedule an online calendar event with a reminder for 25 days after the beginning of the free trial to remind yourself to cancel. They will otherwise keep charging you.