I really enjoyed my stay at Helena's apartment. The space is exactly how it's described in the listing; plus, clean, stylish and containing everything you'd need for a mini-break in Paris. Communication with Helena is straightforward and she is very accommodating when it comes to working around your flight times/travel requirements. All in all, I can't recommend Helena's place enough, I'll be back.
Oh, and Montparnasse is a great place to stay...I always choose it when I'm in Paris as it's a lot less touristy yet still a short Metro ride/ample walk to all the attractions :)