I love MyFitnessPal. It's easy to use, only takes a couple minutes out of my day, and makes me feel comfortable with eating whatever foods I like, while encouraging me to make healthier choices overall.
With that said, it did NOT work for me when I was using the website and didn't have a smartphone. Even though I sit at a desk all day, my phone is the thing that's with me when I'm cooking and when I go out for meals. It's easy and convenient to pull my phone from my pocket and make sure I have enough calories for an item on a menu, for example. And even in front of my fridge it's easier to grab my phone to see what I planned to eat today, rather than open the laptop and sign in online.
I had a completely different mindset and use of MFP when I used the website. It was a chore to go in and enter my data every day, and I would get annoyed with using it and eventually stop, then convince myself it's something I should do, which would restart the cycle. That may not apply to everyone and it may not apply to you; it's just the way it was for me.
I also find it much easier to enter foods from my phone, not only because of the barcode scanner but also because more data about searched foods are displayed before I add them to the diary. Sometimes there are a lot of listings for the same item, some of which have slightly different nutritional contents (presumably versions from other countries) or use a different measurement (grams versus ounces, or cups or tablespoons) than what I'd like to use. The website gives me only some of this info up front, wheras the app lets me delve into the whole listing before adding it.
One thing you might consider if you run into troubles with the website and aren't prepared to buy a smartphone & cell plan, is an iPod touch. You could install the app on that and also use it for music and such. You wouldn't have internet when out and about, but you could always have it with you to know how many calories you have left, and it's easy to make food notes in the app so you can pull up & enter new stuff when you get home. It would save data for anything you've eaten before or have pre-entered. I think that would be almost as convenient as having MFP on a smartphone.
Anyway, you might have a completely different experience than I did with the website, so I definitely encourage giving it a try! Best of luck with it, and best wishes for your weight loss journey.