I haven't worked with either product. I've worked with a polar chest strap in the past. I found that Zephyr offered better software and provided access to raw data recordings. Depending on the nature of your research, you will likely need to have raw data as well as computed values from the device.

Yes, you can use inter-beat interval data from the Polar unit in another program.  I haven't done this in a while, but as I recall, once data from the watch is uploaded to the computer, you can then export the inter-beat intervals as a text file.  This can then be uploaded into Kubios for HRV analysis. 

As M Wilson put it, there is a possibility to upload Polar data to other software. However: does Kubios compute time-frequency analysis? Our Procalysis software supplies all of the above + TFD maps.

I work with Kubios Software. If you transfer your data in a .txt file it would be working.

Yes, you could analyze in Kubios if the format data in .txt. The Polar is the best approach for HRV analysis because this measurements has a high reliability than other monitors. 

I worked with data obtained with Polar, but to use them with Kubios need to remove redundant information (Name, Alias, Gender, ...) and leave only inter-beat intervals in .txt file.

Thanks a lot for your help. The computer we use is not downloading Procalysis due to its uncommon use. And Kubios does show the time domain parameters as well as frequency. I decided to use HRV+ app on Ipad since it is the only one with a txt raw data file can be sent to a computer and than can be uploaded to the Kubios HRV.

We have been using the Bodyguard 2 device from Firstbeat technologies and it works really well. Raw data can be downloaded to any computer and we used Kubios to get several measures of HRV. The study was recently published: International Journal of Psychophysiology 98 (2015) 112–118

You need to extract RR intervals from two consecutive QRS complex and apply the RR data point in Kubios. You need .txt raw data with single column.