These guys here don't need a watermelon knife
Yes, you really need a watermelon knife, but no need to pay that amount for it. Old Hickory makes one for $10.00 and I guarantee it is a heck of alot better than that one.
It can also double as a really big nakiri.
I guess one could use this 31" machete for a watermelon knife. It is certainly big enough. $65 on etsy.
"What happened to those other underpants you had?" -- Flight of the Conchords
I think you'd probably get arrested if you bring that around in Singapore.