Well Neuilly-Plaisance is a suburb in the east of the city. Not to be mixed up with the upscale western suburb 'Neuilly' right behind La Défense.
While it's pretty close to Eurodisney (same line), it will be a pain and very time-consuming, when you want to travel into the center. RER trains don't run as often as the métro does.
Also, it's a lot more costly than the public transportation within the city, because it's out in zone 3.
Carte Orange for one month, zones 1-3, runs at 66.60E (20.30E/week).
That's reasonable though.
Also, at Vincennes stop, the RER line A splits into A2 and A4!! Another inconvenience, IMO.
Neuilly-Plaisance on the A4 leg out to Marne-la-Vallée Chessy (and Eurodisney).
When I travel to Paris by train from Basel, I come from that particular direction. Nothing spectacular those bland suburbs. I doubt, there is much to see, sorry.
Honestly, I'd never rent an appartment outside the city. Imagine, the time you lose on going back and forth and the costs involved. I'd rather pay a little more and stay closer. Also, the owner is probably right that you're only some 15 minutes away from the city. Some 5 stops to Châtelet which is pretty centrally located. From there, however, it's still a way to most of the places you may want to go.
Also, the RER trains don't run as often as the métro and I wouldn't want to use it later in the evening.
Unless I had a very specific reason, I'd think at least twice before renting out there, or in any other suburb for that matter.
In case, you read French, here's the the town's web page:
http://www.mairie-neuillyplaisance.com/