It would work with a mac.But i am not sure if it would be a massive improvement over what you get. I have not used mine in this way so i can't be sure. You will just need either a 3.5mm cable to connect or a usb to mini usb and it will work. I would say to improve the sound quality you may be better off buying a decent amp, but then of course this will cost more. Check what hi fi.com for some ideas. However if you will also use this as a headphone dad with you phone or portable music player i cannot rate it highly enough.
Two rules when buying anything: choose a UK supplier because the Sale of Goods Act imposes the duty to protect the consumer on the retailer, NOT the manufacturer or wholesaler. Secondly, always buy with a credit (NOT debit) card since the credit card company is also legally responsible for protecting the consumer. Also take a look at the Distance Selling Regulations since these entitle you to return goods purchased by mail order or over the Internet at the supplier's expense within, I think, seven days of receipt for any reason. Just not liking them is a perfectly valid and legal reason. Please check the law yourself (Which? is a good place to start) but you will find that the law imposes upon the retailer a duty to supply goods of a fit and merchantable quality and to warrant the goods for a reasonable period. Courts have, I believe, generally taken the view that one year is a reasonable period but don't suppose that on the product's first birthday that the warranty will automatically end. A court may well decide in some circumstances that a faulty product should be repaired or replaced in its 53rd or 54th week. If the manufacturer offers something better then fine but your contract is with the retailer and, where relevant, the credit card company.
Yes, if you use a male-male 3.5mm lead there's no reason it shouldn't work. Its a sizeable enough amp though so it'll make your phone noticeably bulkier if you attach it using the rubber strap provided