Questions asking for recommendations of IoT devices are on-topic, obviously.
As to whether they're permitted, that's up to us to decide. Some Stack Exchange sites, such as Super User, have decided to make a blanket ban on questions asking to recommend a product. Others, such as Unix & Linux, don't see what the fuss is about.
The ban on recommendations on SU has led to the creation of Software Recommendations and
Hardware Recommendations. These sites have a problem connecting askers to experts — it's especially visible with SR which has the lowest proportion of answered questions on the network. Experience shows that it's better to sort questions by topic than by question type: singling out recommendation questions was not a good idea.
So questions asking for recommendations should not be rejected just for that reason. Of course, that doesn't mean that any question asking for a recommendation is fair game — quality control still applies.
Here is a guideline when asking for a recommendation. Questions not following this guideline are likely to be too broad or primarily opinion-based, both of which are reasons to close the question.
A good recommendation question has both some hard requirements and a user story. The hard requirements are constraints (on price, connectivity, power consumption, processing power, storage capacity, etc.) that must be met. The user story allows ranking between candidates that meet the hard requirements.
See also the question and answer FAQ on Hardware Recommendations, and the question and answer FAQ on Software Recommendations.