Just got an email from Signature Solar regarding the 18kPV upgrade offer. For those not familiar yet, If you purchased a 6k or 6500 unit before May 1st you are eligible for a $750 credit towards the purchase of an 18K unit. So as it reads, if you purchased multiple units, you can stack them for $750 each towards purchase. So if you bought two 6k or 6.5k units, that is $1500 off the 18K. You keep the 6k units, but you forfeit the 1-year warranty. Thoughts? Has anyone done this yet? Any issues?