Theft of the idea...for starters.
The 'widget' will have intellectual copyright....if one person thought it up then it is HIS idea, not yours.
If you deliberately replicate it you are violating COPYright...you made a COPY.
See....that is why it is called 'copyright'...the right to copy.
The English explanation is so simple even a knuckle-dragger 'should' be able to comprehend in between drools.
Not every country actually has the concession included in their laws that it is legal to copy for personal use...in fact most cases it isn't....but it is simply not enforced or even practical.
Also....the act of reverse-engineering will have violated any use agreement....usually referred to as an EULA.
When the original sees a drop in sales...he can quite legitimately 'go you' in court...and you will lose. Lost potential income to the original creator will be the first moneys extracted from you.
Then there will be compensation for damage and injury/dilution of his trade name/reputation.
Then there can always be punitive damages imposed for any actual criminality.
'Synthetic reproductions'? Exactly what planet did you fall out of? The written word is also a 'synthetic reproduction' of the author's thoughts....yet it is the latter manifestation that has the copyright attached.
Sure, the music industry WILL change...but like most industries tripping into the 'now-generation' of Internet-speed-dissemination...it'll look like it's dragging its heels.
Rather than spend 2 cents on these debates...save them all up an by legal widgets....don't steal them....