As with any tool, they are only as useful as your knowledge and skill allows.
If you know what it is that you’re looking for, and are observant and patient, these sites can be great at helping you meet the kinds of people you’re hoping to meet. On the other hand, if you’re not really sure what you’re looking for, or don’t know how to read between the lines, you may end up meeting loads of completely incompatible people and burning out in frustration.
That, and the fact that no tool is perfect, tools tend to break and so on.
Internet
is real life. It’s not make believe or pretend, as some people think. It is just a medium. It is the same as talking at a church event, conference, coffee shop, whatever.
Now as for personal experience, the online dating websites have certainly taught me much. They have shown me a lot of people. I’ve been able to look at thousands of pictures, read about personalities, hobbies, expectations, plans etc. Some were unique, some were generic. I could probably run a couple of studies if I committed myself to it (however, I don’t really see a pattern in whom I attract on those websites, as opposed to real life). Generally, the biggest thing I’ve got out of them is expanding my horizons.
I did also confirm my suspicion that it would be very hard for me to find someone anyway. Someone I’d actually
fully (not perfectly but more than just somewhat) click, get along with etc., mutually and with the absence of red flags. Very low probability.
Right now, I can recognise faces in thumbnails pulled randomly out of some several dozen thousand (depending on how many out of all female users upload photos). I can very easily recognise patterns in profiles. And yet, profiles don’t do it for me. Yeah, a nice person, would be great to meet, I would be suggesting having a coffee if we were from the same city and could keep it to just a coffee (and if I can avoid first name basis, I do it), but no compelling reason to buy a return ticket book a hotel for the night etc… Can’t really keep up a normal, friendly acquaintance, devoid of dramatic, heavy epistoles and de facto relationship (with each of such “pen friends”) building regardless of the absence of a formal relationship.
Also, choosing among several people with attractive but not compelling or even compelling but not conclusively decisive profiles, would be somewhat awkward. I’d feel bad setting up a semi-dating routine to “try them all out” (even the concept itself should make a gentleman cringe, I believe), and I totally reject randomness (or semi-randomness, like “the first one I come across”, where you have a defined procedure that leads to a conclusive result but the outcome is still random in relation to substantive issues).
All of the above in spite of the fact that I can actually very well imagine myself knowing that I want to marry a woman after talking to her for two hours at a cafe, even without any immediate romantic sparks present. In fact, I can imagine myself having gathered sufficient data to propose within that time-frame.

Still, in most cases in practice, you just see an attractive but not compelling person and you gotta choose. For me, that’s not enough. I need to know why I’m making this choice and not that one, and randomness or the order of appearance is not an answer I’d accept.
On the other hand, plenty of folks have noted success with dating websites. In my case, I’ve learnt a couple of interesting biographies and made a couple of short-lasted but very interesting acquaintances, from a human point of view, not just romance. In one case maybe I regretted that nothing came out of it but I suppose it was for the better.
Ehhh… I’m all for meeting people the old-fashioned way, but outside of some of the more lively, urban areas, few communities have many young, practicing Catholics. Even at that age.
Same what you said.
Standard-issue advice: not all’s gold that glitters. People tend to look better in $100 professional photos than in self-taken mobile phone photos. Everyone can look like a celebrity with the right make-up and lighting, then again you’ve probably seen pictures of celebrities without make-up. Very ordinary, some of them, aren’t they? This works the same way for everybody. If looks are important to you, make sure you see a couple of pictures, from various angles, and not only blurred or otherwise artistically tampered ones. Pay attention to those that nobody was paid to take.
(By the way, pictures
can express character and a lot of other things, although not conclusively.)
If you see fields that are lefty empty, they may be empty out of forgetfulness or lack of care or whatever similar reason. On the other hand, they may indicate a rather complicated outlook (e.g. when on Catholic dating website the field “opinion on premarital sex” is suddenly left empty, even though divorce and contraception are filled in). Don’t be paranoid, don’t be naive, either. And you can ask. Generally don’t hesitate to get to know someone without the pressure to woo him or her into a relationship. If you can keep it light, then all the better.