1. What’s your experience been like so far using the KizON?
Positive! It's a useful tool in a parents arsenal of gadgets to help ensure the happiness and safety of their children.
2. What’s your favourite feature on the KizON?
To be honest I like both the tracker and the inward/outward calls as features. Together they make me feel like DD1 is a bit safer.
3. How helpful did you find it being able to reach your children while out of sight?
Very helpful. I'm a WOHM and during the holidays DD1 was at kids club or staying with family. I had no reason to doubt she was safe, but being able to just look up where she was every so often gave me a warm feeling of knowing I was able to check up on her unobtrusively. She's not prone to being homesick, but if she had been I knew she could have easily reached me.
4. How easy did you and your DC find the KizON to use?
Relatively easy. The app installed without any problems and I was able to easily connect up my phone as the primary contact. I haven't registered a secondary contact yet, as I'm not sure whether there's any way to remove or amend a contact? I couldn't see anything about it in the instructions.
Also, I anticipated that only Android phones would be able to be primary/secondary contacts and install the app, but is it limited to Android for guests as well?
DD1 spent half of the trial time with her DGrandparents over the Easter holidays. I set DGrandad and DGrandma up as guests, but only DGrandad's Android phone would connect - DGrandma's Apple phone went straight to voice mail.
However, I'm not sure whether this is because DGrandma has her number is set to privacy so doesn't appear when she calls? If it's due to the latter, it might be worth including in the instructions that numbers must be visible when calling for the device to accept them.
5. How often did you use the device throughout the trial?
More than I expected. I used it to keep tabs on where DD1 was, which was especially useful on the day she was returning with DGrandparents as I could track where their car was as they meandered up the country!
The week before, she also used it on several days to contact me on the way home, as she gets picked up by DH who then co-ordinates to meet up with me and DD2 on route. DD1 loved her special job of calling me to let me know where she and DH were. 
We had a few days out over Easter, and while we didn't have any necessity to use the device features, it made me feel more confident in letting DD1 roam a bit wider. I can see it being particularly useful for days out, especially when they're likely to be crowded.
6. What did your DCs think of the design?
She liked it very much, she was all proud of having her own special phone to use. The first few days she got a bit overexcited and spent a lot of time calling me (or leaving giggly voice messages) but that calmed down once the initial excitement was over with.
The device as it's currently designed is a bit bulky on her wrist and doesn't sit well, as it's longer than her wrist is wide. If the size cannot be reduced then I'd suggest rotating the strap 90% so that the length of the device sits along the arm rather than across it.
The pink and hearts design was fine for DD1 (who is nearly 5YO) but I agree with others that it might be a bit childish for an older child. I'd like to see more gender neutral designs as well.
Suggestions
I would like the voice to have a British accent. The American one sounds horrible!
It might be a good idea to have a version with two buttons, clearly numbered and/or marked with different colours, to call each contact. If only one contact is set up, then either button could call the primary contact. DD1 I expect was one of the younger ones in the trial and I'm sure she could handle being told that "Blue is for Mummy and Red is for Daddy" or similar.
Having two buttons would also mean that for switching the device off or similar, you could press both buttons together. Means it's less likely for the child to do by accident and means it won't sound like you're trying to make a call.
With just one button, in the config I'd like to be able to set an amount of time it tries the Primary contact before the Secondary contact. I need my voicemail to be active, but it'd be good if I could set the KizOn to give up and try a Secondary contact before my voicemail kicks in.
For really complex, it'd be great if it did the same for the Secondary contact then went back to the Primary contact if there was no answer and DID allow it to go through to voicemail if there was no answer the second time. Hopefully that makes sense-!
A small display would be useful, which could display the time by default and possibly an indication of battery. Then it could display either a graphic or simple text when calls are being made to/from the device, configurable via the app. So it has
or "Mum" when contacting or being contacted by the Primary contact, and
or "Dad" for the Secondary, for example.
As others have mentioned, an indication of remaining credit would be useful in the App.
Also, voicemail needs to be turned off on the sim in the KizOn - as there's no way for the device to reach it, but having it accept a message makes the caller think it will.