Good alternative.

Use threema been more than a year on a "HTC One M7". So far without any major problems. Handling eigentl. as usual, no larger change than the average consumer needed. Over time, now just under 3/4 of the old WhatsApp contacts now (also) at threema, the rest runs via SMS because with me whatsapp- (and facebook-) -free zone. Since the other must stop.

Reason for the use of threema my part is the idea that not everything or as little as possible from what I should be public disk, even if I have nothing to hide.

Delivery of Nachichten usually takes place without major delays. Very often the reason for delayed delivery of messages to the settings on the phone (eg standby) or on mobile network. Look chic (material design), update Android 5.0 (Lollipop) took place without any problems, Push works reliably. Many settings poss individually. (Eg telephone number or the balance. Plugin for voice messages). Improve the group function and multi device (using an ID / user name on different devices) would be nice.

Threema has proven to me as the first alternative to WA. In other alternative messengers have / I had not so much long range or contacts.

What to look for: After reinstalling / initial set of threema-account (s) Backup / backup at least the ID (user name) perform as threema operates independently of the (mobile) phone number. Therefore threema can also be used on the tablet, however threema is not (yet) Multi Device capability (using an account / access on different devices).
Another advantage is that you can change phone numbers in his (s) old (n) - previously saved (n) - use ID / username continue.

That threema when purchased version here (ie via Amazon Shop) requires the appropriate connection via Amazon app, is likely to be similar to Google / Android with the PlayStore be (my type of business). Who does not like may refer the file directly from the manufacturer.

So now a lot of fun trying. For me, the 1.99 EUR paid off and were a good investment. Although at threema (still) is not testing possible: at the price range of many of the mobile phones used here likely 1.99 EUR not tear a big hole in your wallet.