Bundles or box-sets?

First box-set of my duke books. £1.99

I have ventured into a new market – that of publishing my books in a box set – or is it a bundle?
This way anyone who hasn't read my books has the opportunity to pay for two titles and get a third one free. Not quite BOGOF - but a similar idea.
As always Jane Dixon-Smith has made a beautiful 3-D cover for me. It remains to be seen if presenting my books in this way is something my readers want.
Everyone loves a bargain – so I'm hoping this will tempt some new Regency readers to try something different.
I noticed on Amazon that some authors call these groupings "bundles" while others call them a "box-set". Some have 2-D covers, others 3-D (like mine) and a few just print titles on a single cover and hope for the best.
My last post was about titles and their importance to sales and I think that having a professionally designed cover is equally invaluable.
Do you buy books with amateur covers or does this put you off? My first book, The Duke's Reform, originally had a cover I designed myself – okay – but obviously not done by a professional. However, this book sold hundreds of copies with this cover so it obviously didn't stop people buying it.
I think the time of year has far more influence over sales figures then either cover or title. June and July is when people are going, or thinking about going, on holiday and ready to buy extra reading material. February – the most gloomy month of the year – is when nobody has the inclination or time to read anything new – probably because they are recovering from the financial excesses of Christmas.