Why is that a factor? If you need a transformer capable of delivering a certain wattage, then it will weigh whatever such a transformer weighs.......... Now, I don't know exactly what an egg/muffin toaster draws in current, but 1.5kw is probable. It may even be more.
Sorry. Need to know what wattage the appliance will draw before anyone can answer this. This will be on the maker's plate on the appliance. It may also be available on the web, but I didn't find it on a quick scan of the website you quoted. An email to them, perhaps??
Only when we know what wattage the thing is, can we advise (or, can you work out for yourself) how *big* a PSU you'll need.
FYI: My UK spec. Dualit toaster is rated at 1700 Watts (1.7 kW) at 240 Volts. (Watts are also known as Va)
Use too small a PSU and you'll kill it. Use too big a one and it won't matter a jot.