It doesn't look safe to me. Although it might not be barred there are still places a hamster could get a leg caught, plus it looks very flimsy and could fall over easily while being used. It is also far too small for a Syrian hamster. Even a dwarf hamster needs at least a 6.5" wheel.
The tried and tested wheels in the Uk are the Wodent wheels, Karlie Wonderland wood wheels and Trixie wheels. You'd need 8" (20cm) for a dwarf and 27/28 or 29/30cm for a Syrian hamster. There is a 6.5" silent spinner which is dwarf hamster sized but there seems to be a problem with these not spinning since a manufacturing change.
These are the trixie wheels
Trixie Exercise Wheel, 28 cm Dia (colours may vary): Amazon.co.uk: Pet Supplies
These are the Karlie wood ones (29cm out of stock right now)
Wonderland Exercise Wheel: Great Small Pet Accessories at zooplus
The wodent wheels are available from pet planet
Wodent Exercise Wheel - Junior on Sale | Free UK Delivery