@ameo___
I've been looking for something like this for awhile! Most recommendation sites I've seen based on MAL profiles tend to just factor in whether or not you watched a series, rather than how you rated it, so I'm glad to finally find something that should, in-theory, recommend me stuff based on my actual tastes!
Without having seen any of the anime on this list, because, well, they wouldn't be recs if I'd already seen them, I'd say the non-preview site's recs feel like they'd be "better" for me, for the most part.
Samurai Champloo (which has a lot of the same creative staff as Cowboy Bebop, which I loved) is on the non-preview site's recs, and even says the reason is because I liked Cowboy Bebop, the Cowboy Bebop movie and Baccano! (which, while unrelated to Bebop is an anime I liked for much of the same reasons I enjoyed Bebop).
The non-preview site also recommends Millionaire Detective because I liked Moriarty the Patriot and, without having seen Millionaire Detective, just feels like that's probably a pretty safe bet.
When I turn on extra seasons, the non-preview site's top recommendation (or, at-least, the one at the top of the list; I'm assuming the recommendations are ranked in some way, but of-course I'm not sure. Even if I looked at the open-source code, I'll openly admit I'd be too math-illiterate to understand most of it. ^_^;) is Free! Season 3. And, yeah, I think it's very safe to assume I'll like that one, since I loved the previous 2 seasons. It does show-up on the non-preview version, too, but much lower down the list.
I will say, though, the fact that the site factors in the one anime I dropped without a rating as "Because you disliked..." could be a double-edged sword. In my case, that anime is one I am never going to watch, so it's not exactly fair to say that I "disliked" it. But I know that most people who drop series without ratings are doing so as a way to say they disliked the series, so that's definitely just a me thing.
Both versions of the site place Corpse Princess quite high on the rec list, so I might check that out soon. I've been looking for something to watch soon!
Out of curiosity, I also tried the site with my IRL best-friend's MAL username, since I think I know her taste pretty well and have a fair guess about whether or not she'd like a given series that I've watched. Both versions of the site only return a few anime I've seen when using her username (those being Death Parade, KADO and Hanako-kun), which isn't a large sample size, but I suppose that isn't surprising since we've watched a lot of the same series, lol.
The preview site recommends Hanako-kun for her, and the non-preview site recommends Death Parade and KADO. I imagine she'd enjoy Hanako-kun and Death Parade, but I *think* she'd probably like Death Parade more, for what that's worth. Honestly, I could see her going either way on KADO. I have been surprised by some of her anime rankings before, though, so maybe she would prefer Hanako over Death Parade? XD