we stayed the full time of our visa free entry. There is absolutely no rule that you can only spend a few days here and there. In fact with the two land entry rule you are forced to stay in the country longer. We would prefer to travel in and out of the country more
If you are going to be leaving many times a year best to go with visa free entry and extend. You have to pay a fee to come back in if you have a visa so if you are planning on leaving anyway don't waste your money