Not bad at all. A couple of minor suggestions: Make the free delivery more prominent. £13.99 is the full price. Also, it would be beneficial to show us how much we're saving - compare it to the B&Q price, Homebase, etc. Your testimonial tells of next day delivery: this is a big selling point and should be pushed more aggressively ("90% of orders delivered next day!", or something similar.) I'd consider replacing the "Add to Basket" text with "Buy Now". You've only got 1 product, so the basket is kind of redundant.
I disagree with Sysops though - how many first time foam gun buyers are there out there? Most people who use these tools have used them before, are simply buying a replacement, and already have the accessories. By all means, bring on the extra products, but their absence is not a deal killer. There's nothing wrong with single product websites as long as the market exists.