The trials - undertaken since 2016 - cost ratepayers $120,000 for consultants, who reported the device gave 80 per cent coverage on the Coromandel.
But in a report to the council at its May 12 meeting, councillors heard the consultant's report could not be relied on to give adequate information to make a decision.
An independent review by Kordia Ltd said at least 300 or more homes should have been trialled.
The reported reception levels, based on FM commercial radio station signals, was "anecdotal" and the trial sample was far too low.
"For Cook Beach/Ferry Landing, only three out of a population of 5857 have been sampled. Estimating 100 per cent indoor coverage for this entire area is not valid, even if 100 per cent of the three locations were successful," Kordia's peer review author said.
The trial was supposed to show how the device performed when located indoors, but Kordia said that, based on comments in the consultant's report, it was unclear how many of the 95 locations were taken indoors, and how many were taken outdoors.
"Though it may be possible that potentially 80 per cent of the overall population on the peninsula can receive the IAD Alert Radio service indoors, there is insufficient information or measurements provided in the report to conclude with a suitable degree of confidence that the 80 per cent estimate is valid or can be acheived, or how reliable the service would be," it concluded.
After questions raised by Councillor Gary Gotlieb, a decision to progress a business case was deferred to June-July. More detail on costs was requested by councillors.
The council has since announced the project will be discussed and reviewed at a closed workshop.
Resident Vicki Ovesen, who has been following the project, says communities wanted assurances that they would get clear communication in the event of a tsunami.
"This device is only for indoors, needs a strong FM signal, untested technology, etc - which outweighs the risk and cost of implementation," Ovesen says.
"In an emergency, there needs to be a group of systems in place like sirens, alerts, information via radio, internet, TV if there is electricity and trained locals with knowledge of procedures, community education.
"Putting all your eggs in one basket with one device is no use if those others aren't operating correctly."
The technology has not been taken up by several other councils around the country.
In Tauranga City, councillor Steve Morris says the community had requested a system for almost 15 years and its council will instal 12 sirens for $1.8 million.
The Tsunado device did not stack up, he says, due to the number of houses that it would need to be installed in.
"The community was really saying 'Give us our sirens'."
Morris is a former chairman of the Papamoa Ratepayers Association and acknowledges large districts like Thames-Coromandel are geographically challenged with having to reach all towns with the same system.
"What we found was local philanthropic funders were prepared to step in because it's a civil defence thing - it was a lifesaving thing."
