Claiming to have 400-600 lumens and 1080p resolution on a projector less than £100 should set your warning bells ringing if you've read our buyer's guide to fake amazon projectors.
The YG-300 portable projector is cheap at a price of around £30, but minus amazon costs at between 7% to 15% and 10% advertising costs, to name a few, the projector itself must have been built for around $5.00. Hardly a quality projector fit for home cinema, $5 can't buy anything powerful enough to project at 400 lumens, let alone in 1080p. 
Always read the long descriptions for products like this, as they are full of disclaimers. The actual resolution is quoted as 320*240, Not HD, instead of 1080p as it often says in the title and amazon specification table. When a retailer says the mini projector is "to be used in a dark room", steer clear as this usually means the lumens are actually so low they cant be seen in a normal room and its around 10 to 50 lumens only if you are lucky. These types of products sometimes overstate the actual brightness by 20 times the actual brightness!
If you want a trustworthy mini projector, there are plenty of reputable brands to choose from such as Pico Genie, Vivitek, Acer, BenQ, CHiQ LG and more. If you're looking for a pocket projector that has between 400-600 lumens then why not try the Pico Genie Polar, the Polar has 500 Ansi lumens which will give you a great image even in ambient light.
And If you want Full HD splendour on a powerful battery powered projector of a capability of 600 Ansi lumens of brightness then the Qumi Q38 has got you covered.