You should try to engage people using social networks, it is easier to spread than email. The conversion rate on emails are low but is still a valid tool for that. Send and email with a simple and objective message that will make people want to try.

The best way to have feedback from users is to watch them use the app. You should put them on the hands of everybody that you can and without any instrucions and just watch, don´t even say that the app is yours. Try to do it a lot.

If you want feedback from others, you can include the feedback form inside the app and suggest users to answer occasionally.

I would also strongly recommend to use a tool as Flurry Analytics. Is the best way to get data from how is the use of the application.

Pay attention to those data and be open to change your app a lot, you may need more features or cut some off to make it easier to use.

If you need more help please contact me.

You need early adopters of your app - your friends or followers via social media. Otherwise I'd try to contact some testing company to provide some beta testing.

You're going about this wrong and a lot of the advice here is also wrong, by worrying about the consumer experience first. Stop what you're doing and get out and talk to restaurants.

Make sure that restaurants are willing to offer rewards, and get signed commitments from at least 10 restaurants that they will do so, based on the metrics that they define matters.

Next, use the restaurants' existing social media outlets to get their own fans signed-up into private beta as an "exclusive privilege" to their fans.

If you can't get restaurants to do those two things at this point, you have a high likelihood of failure should you pursue development of an app without this important piece of customer development complete.

Happy to talk to you in a quick call to provide more details about what I'm describing above.

When the waiter asks if they want dessert, he should also drop a card with URL/qr code to the app.
Depending on your flow, it will point to your landing page or directly to testflight (where they register to download the beta, you get their email also from here).

They key is to have real early adopters.
With this system, you:
- make it easy to discover the app
- give them a chatting/funny topic (will remember experience)
- have "true" adopters since they are at that restaurant

...might also suggest to snap a picture with a restaurant mascot for the picture they share related to their dining experience.

Signup 5-10 restaurants as your test group, give them freebies to come on board. Thereafter end users. Period!