I have looked on this companies website and all the properties they have are in the Estepona region around Manilva and Casares.
This area has seen a boom in property prices bigger than the rest of Spain. Bigger than the Costa del Sol around Fuengirola and Benalmadena and so this area will have "peaked" for the moment. If I were looking to invest in a region like Manilva then I would want to be satisfied with two points.
1. Is the area a new development area which would mean that my purchase is one of the very first developments in that region. Then I woud look at buying for future investment growth but little rental.
2. Is the area a well constructed area where all the developments are complete and the area is now just having "filling in " developments in pockets of land. If yes and I like the area I would buy for future investment and current rental.
The area your friend is buying in is right in the middle of the two points above so my advise would be, Do not buy. Your friend will not get a rental coverage for their mortgage from this area and the only way a company will offer guaranteed rental is by inflating the original purchase cost ( beyond the rental income so more profit for the developer). When this period ends your friend will struggle.
The Estepona region is to far away from Malaga airport and until a new airport is constructed then people will not be happy to travel more than an hour from Airport to Apartment. Gibraltar is close by but very limited.
Although the Costa del Sol has seen large increases in property, it is still a good area to buy in for the long term investor. But you either look at an area along the coast within 40 minutes of Malaga airport, where you have good shops and facilities that tourists want, or you go inland to a one hour maximum and buy a property in a rural area but with facilities close by ( 10-15 minute car drive).
I hope this advise helps and may I offer your friend good luck and best wishes with whatever they choose to purchase.