When wife and I chartered in St. Lucia we did Sun Sail. No problems with them. Never heard of the company you cited.
St. Lucia is okay but we would recommend other Caribbean Islands first only because of certain experiences with locals while at anchor in certain areas and on last day in town.
we have not chartered with Oasis Marigot but when our charter was over we spent 4 days at a hillside villa at Oasis Marigot. The accomodations were wonderful and overlooked Marigot Bay. (One of the best views in the Caribbean) As far as sailing St Lucia Marigot Bay and Soufriere at the Pitons are not to be missed. We did not do more than those two locations because we were bareboat chartering for 2 weeks and also did the Grenadines St Vincent Canouan Mustique and Union Island. If you do not do this trip you are missing the most beautiful part of the Caribbean. The sailing is longer (not like the BVI) but less crowded. We encountered "boat boys" who can be a nuisance or can actually be of some assistance depending on the situation. Do not let this possible irritation dissuade you from a great area to cruise