When comparing WhatsApp vs Reach, the Slant community recommends WhatsApp for most people. In the question“What are the best messaging apps for iOS?” WhatsApp is ranked 8th while Reach is ranked 29th. The most important reason people chose WhatsApp is:
The interface is very simple, fast and easy to use. You can start using it as soon as the app has been downloaded - it does not require setting anything up or registering. You can communicate with anyone in your contacts list that also uses WhatsApp. Includes useful features like seeing when a contact is currently available or typing.
Specs
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Pros
Pro Straightforward interface
The interface is very simple, fast and easy to use. You can start using it as soon as the app has been downloaded - it does not require setting anything up or registering. You can communicate with anyone in your contacts list that also uses WhatsApp. Includes useful features like seeing when a contact is currently available or typing.
Pro Widely used
WhatsApp reported 1.5 billion users in 2018. Your friends are most likely already using WhatsApp, so it's easy to get setup.
Pro Effortlessly builds your contacts by using your phone number as identification
WhatsApp will automatically find all of your contacts currently using Whatsapp and add them to your contacts. This makes it really easy to setup and given that it's the most popular messaging app it's likely that a lot of your contacts are already using it.
Pro Message mirroring on web app
WhatsApp can be used from the desktop via Chrome, Firefox and Opera browsers. Accessing it requires using the Android app to scan the QR code that's presented on web.whatsapp.com.
Pro Signal protocol
Whatsapp uses the state-of-the-art Signal protocol that ensure strong end-to-end encryption.
Pro One-on-one texts can be encrypted
WhatsApp has implemented end to end encryption for messages sent on it's service. Even WhatsApp has no way to read a users messages.
Pro Mass message multiple people at once
Ability to send a single message to multiple people without exposing their contact information to each other. Reach sends individual messages to the group rather than starts a group chat.
Pro Personalized and Individual conversations in "Group Mode"
When sending a message to a group of people, Reach starts a private conversation in your Messages, Mail or WhatsApp apps respectively for each recipient
Pro Reusable Recipient Groups
Improve workflow productivity by creating reusable recipient groups
Pro All platforms in one: iMessage, Text/SMS, E-mail, WhatsApp, and Google Voice
Reach does not require the recipient to have Reach installed on their device. Instead it uses the existing messaging apps on the device to send the message to the recipient.
Pro Message Templates Feature
Prepare message templates which can be reused. Message templates can have recipients name variable, for example the template "hey {first name}!" will be populated with the recipients first name when the message is sent out
Pro Free texting through Google Voice
Reach integrates with Google Voice and allows to send free text messages in the U.S.A and low rates across the globe
Pro Fully automated mass texting with free SMS
Using Google Voice integration, Reach is able to send mass texts in a fully automated mode (without the need to press "Send" button for each message)
Cons
Con Shares meta data with Facebook
WhatsApp shares your messaging meta data with Facebook if you do not opt-out in the settings. If you use the same phone number for WhatsApp and Facebook, the profiles can easily be linked.
See https://www.whatsapp.com/faq/en/general/26000016
Con Tied to carrier phone number
WhatsApp cannot be used by people without a smart phone with an active cell plan. If your phone is lost or damaged, or if your phone number changes, you cannot get messages sent by friends without them updating your phone number. You cannot send message to them until you are able to get SMS messages at your phone number.

Con Proprietary
Not open source.
Con Hard to migrate history cross platform
Migrating your chat history from Android to iOS or the other way around is not so simple. In some cases it requires a 3rd party app and in some the only way is to migrate specific chats one by one.
Con Web interface uses message mirroring
To use your computer to send messages your phone must be on with a consistent data connection.
Con Single device
You cannot use the same WhatsApp account on multiple devices (e.g. a tablet, a PC and a cellphone). The account is tied to the device with the specific cellphone number. Chat history is deleted when you sign in to a new account, unless you have created a backup.
Con No cloud sync
Messages are not stored on WhatsApp server for privacy and security reasons.
Con Limitation on shareable file sizes
WhatsApp now allows users to share files of any type, but there is still a 16 MB size limit.
Con Need to press "Send" button per each recipient
When sending a message to a group, the user must press "Send" button for each recipient. The only work around is to use Google Voice integration for fully automatic mass texting
