Incorrect. In fact for specific issues a 3rd party dialer is actually recommended: Huawei Ascend 5W Can't Call over WiFi – Republic Help
3rd party dialer apps should not be recommended same as 3rd party text message apps. There are too many out there that can do different things to circumvent the phones stock telephony API. Many could use there own VOIP service, like Google Voice Dialer that would interfere with or not support Republics service. As far as I have read, Republic only tests and supports the phones stock dialer app(unless otherwise specified).
For what it’s worth, I’ve never had an issue using a third party dialer with Republic’s service on legacy or current phones. I’ve also never found one I like better than my phones’ stock dialer. Finally, as @louisdi points out in the case of a specific bug with Huawei’s Ascend 5W, use of a third party dialer is the only viable workaround available.
Furthermore, VoIP apps generally do not interfere. If they did this wouldn’t be possible: Calling International Numbers with a Republic Phone.
I have tried a few random 3rd party dialers. And they only result in Cellular calls. Do not do wifi calls or allow for handover.
Can you share those that you’ve tried as I tried a whole bunch and have never had that issue. In fact the recommendation for using a third-party dialer with the Ascend is specifically to allow for Wi-Fi calling.
There were several, the only one I recall liking was TruCall or TrueDial or something. That was done on my Moto X Pure when I first tested R.W out and I was told NOT to use 3rd party dialer apps or text messaging apps. That phone now has a custom rom and no way to pull up its history of installed apps.
I recalled not recommending true call app as it was more than a dialer it also wanted to replace the texting app and at the time I did not see a way to switch it to use system APIs
None of this changes the fact that the dialer portion of Truecaller works fine, as does hiya, drupe, dialer+ and marshmallow dialer. I’ve yet to find a dialer that does not.