We stayed at Yael apartment for 5 weeks during trade fair. It was very convenient to get to Parc des Exposition by RER B, and one more advantage - Les Halles station is not that crowded as Gare du Nord. For those, who come for city attendance, all highlights of city are just nearby. So location is great.
For apartment itself also only positive feedback. It is very convenient, light, and windows face inner yard, so its very quite. There is enough place to put your things.
I'm very satisfied with this apartment, and I will definitely want to stay here again during our next visit to Paris.