First off, I'm a satisfied new customer w/ Isaac and his products. Though I have limited experience with just IO6 atty's and IKV 510 carto's - both my wife and I like them over others we have tried in the last few months. This said, I offer this as constructive feedback not from being disgruntled.
I think improving communication and attention to order details would help (again speaking from my limited experience w/ IKV).
My 1st order of 2 IO6's and some carto's had a mistake. One of the IO6's was not the ohm rating I ordered. I contacted Isaac via the website contact form and it took a couple days to hear back. He said he'd send me the correct one. I replied - hold off on sending it - I'm putting in another order, you can just send the replacement with the next order.
Next order arrived and - whoops - the replacement atty was not included and 1 of the drip tips was the all black IO6 top not one of the colored ones. It took 3 days to get some kind of reply from Isaac. He said he included the black one instead as he thought I'd like it better. He was right, but a note in the order shipment saying he did the substitution would have been nice - then I would have know it was not a mistake - but him trying to be helpful. Oh - also said he'd ship out the replacement IO6 atty.
Got the 'replacement' package in the mail yesterday. huh! It contained 2x 510 IKV 2.5 ohm atty's when I was expecting just 1 IO6 2.5ohm atty replacement. Yikes! What am I to think - was this another error or does Isaac think I'd like these better than the IO6. (to be complete, he also included the b&W colored tip that he substituted with the black one)
At this point - I'm just going to erase the slate and start again. I haven't tried the 510 IKV's so I'll give one to my wife and one for me to compare to the IO6's we've been using. Then I'll order some more IO6's and some of the RY4 I see people talking so well about.
So, I hope the 'reader' can see I'm trying to help customer satisfaction and not being a whiner and complainer as overall I'm satisfied and will be placing my third order in as many weeks.
PS:
Now this is selfish - but being about 30 minutes from IKV's location, I'd surely wouldn't mind customer pickup instead of waiting for the mailman