I am currently in Costa Rica having completed a few weeks of language classes with CPI. I came with my family and spent time at two of their campuses plus went to the family camp in Tierra Magnifica. If you want to learn Spanish, I cannot imagine a better way to learn the language then a few weeks with CPI in a homestay. The teachers were very good for all of us and I learned more Spanish then I remember from two years of college Spanish. The immersion experience was a great way to learn how to converse with others in Spanish. I wanted my children to get some basics and they are now conjugating verbs in both present and future tense. I am impressed.
However, the housing can either be great or difficult. Our 'homestay' in Flamingo was actually in a small hotel. We had breakfast and dinner with our 'mama tica' and she tired to help improve our language skills. She was also very concerned when that the kids had food they wanted to eat. However, the lack of hot water and air conditioning was tough for a man of a certain age. My kids did not complain until there was heavy rain which washed out the water line to the hotel. Our last two nights we had NO WATER. This means no showers, no toothbrushing and no toilet! I mentioned this to CPI who did not appear concerned. Since it was the last two nights, we just let it go. I knew a homestay could have problems but this was much worse then almost anywhere I have stayed before.
On the other hand, the apartment in Monteverde was great. Two bedrooms, a kitchen and two bathrooms were perfect for the family. We had water and electricity almost all the time and the wifi was pretty consistent too. (The wifi and electricity were not always available but CPI helped fix the problems as soon as they occurred.) The apartment was cleaned daily and they included free, good coffee.
Overall, I highly recommend CPI as a school. However, the housing can be great or difficult. A homestay is probably the best way to get a true immersion experience. However, ours was not something I would ever repeat. It may be ideal for a college student or the truly committed language student. I would not recommend it for anyone who likes to have hot and cold water on a regular basis.