It is a good item to have around, especially if you have a tripod or head that doesn't have one. Can use it for other use too like making sure your tables and pictures you hang are level. :bsmilie:
The original Manfrotto 2 axis bubble level costs about $60 which is too much for a small bit of perspex and coloured liquid in my opinion. The unbranded ones at OP are identical and costs about $24, which is a lot cheaper in comparison. Maybe someone can DIY one from those sold at hardware shops.