Diamante K will be a great choice for some travelers and a terrible one for others. If you want to be away from the madness of the Tulum scene, and are seeking a peaceful spot in the midst of nature, this is a pretty good choice. The property is clean and the staff are helpful. The views out over the ocean are lovely if you can mentally screen out the huge mounds of stinking sargassum. The restaurant is excellent, but far too pricey for the average eco-tourist.
Travelers who want comfort and beach amenities will not find it here, at least in the summer. There is no AC and the rooms are stifling despite the small fans mounted inside the beds. The pool is poorly maintained. The tiny beach area is totally swamped in sargassum--you would have to wade out through a four foot deep sargassum sponge to get to water, and the entire area is fouled by sargassum fronds out to about 25-30 feet from shore.
If you like being inside a national park, this place fits the bill. Just be aware that every time you enter the park, your car will be searched by police for alcohol or plastic, you will have to pay a hefty entrance fee (EVERY DAY) for the national park, and there is only one road in and out.