Having owned both, I can say with some authority that these two pedals are not at all alike. Zendrive is a smooth, somewhat compressed, low-to-medium gain overdrive, best suited for playing single-note solos. The Zia is a low-gain, crunchy overdrive best suited for Stones-ey rock 'n roll rhythm guitar playing. The Zendrive has a bit of bass loss, while the Zia has, IMO, too much bass response, and can sound a bit flubby and raw.
I won't comment on the Zendrive, but I will say that I was not too impressed with the Zia I had owned. It got replaced by a barber LTD SR, which I think does a far better job doing the low-gain crunchy rhythm guitar (and also slightly overdriven leads) thang. With all due respect to Durham Electronics, however, I do own their SexDrive (clean boost with subtle compression) and that thing is never leaving my board.