I spent a week in Samara and a week in Heredia. The school and teachers were all great. The classrooms have electronic white-boards, the number of students in each class is kept small. I was tested when I first arrived and the evaluator put me in the correct level right away. As a school this is a well-run operation where you can easily learn. I studied with students from all over the world.
The campus at Samara is well-kept, right on the beach and the town is small so you can easily walk to shops and nice restaurants. The local beaches are pretty awesome and usually the waves are about right for beginners to learn to surf. The campus in Heredia is a nice oasis in kind of a gritty city. As an older guy I felt relatively safe alone but I would recommend that females keep in pairs or groups. I had to decline offers for drugs twice while just walking around. Just use some street-smarts and don't look for trouble, you should be fine.
I utilized the home-stay program arranged by the school for both weeks. Don't expect luxury, it's not the Four Seasons. It was a great way to be immersed in the culture and learn how people live there. I was greeted warmly and well-fed by both Tica families. I only wish my spanish was better so I could have conversed more.
I went in March and I never saw a drop of rain for two weeks. Samara is quite hot, Heredia is at a higher elevation so is much cooler and plenty windy. If you have never been to Costa Rica I recommend spending time at both to get the beach experience and city experience. Travel from the USA is pretty easy, the San Jose and Liberia airports are modern, clean and have multiple airlines running service.
Taken as a whole this is a worthwhile experience and not particularly expensive. I have recommended it to people I know who are looking for a good way to improve their spanish.