We stayed for 1 month and found the apartment to be as described and well equipped for a stay in Finikas. The balcony is a lovely place to sit, although we did miss not having a slightly bigger table to use, but it's a minor point. The place is 5 minutes walk away from great beaches. The pets (cats/dogs) were lovely to have around and we'd particularly recommend Finikas for your trip to Syros if you prefer a less touristy environment.
In terms of tips for your trip, we recommend the first bar you reach on the corner in Finikas, the Calmo Mare cafe/restaurant for Mezze and especially The Meltelmi taverna in Agathopes (15 mins walk away) which has a very nice owner and great locally grown food. 10 minutes walk inland from Finikas town centre are an excellent greengrocer, butchers, and (most importantly :-) a gyros shop. There's also an old fashioned bar, at which we can recommend having the 'half litre wine/ouzo and mezze' choice which although cheap is surprisingly generous and will probably be enough for dinner!
Another tip not well publicised is to walk between Finikas and Galissas and then onto Kini along the hiking trail (we just used google maps which found the route) - good only if it is not too hot of course. Hope you enjoy your stay.