Both sellers seem to be of a high standard. those ratings are very good for a company with that many transactions.
Bear in mind that the first one (urgalaxy) offers a 'no VAT / duty' guarantee, so that if you get hit, then they will cover the cost. The other one leaves it to you to pay it, if necessary. This could make a big difference!
Many parcels get through without charge, the customs just take a number at random to charge as they don't have the manpower to check every parcel. However, there is a reasonable chance of being hit and could come to a fair amount with this item (around £100 with collection fees added). The actual charge assessed can be very hit and miss and often they charge more than they should, I have twice been charged the VAT and duty percentages using the dollar amount as sterling (i.e. a $50 dollar item is charged as if worth £50 not £25). I can tell you now, the paperwork and appeal process makes it not worth kicking up a fuss about unless a quite high value item. I think they try to get you to give up before getting to the point they give you your money back.
Having a repayment guarantee saves worrying about the possible extra cost.