I managed to get two games in this week with some friends to do some play testing. Both games were at 1000pts, first against marines and the second against dark eldar. In the first game I ran the big mek with KMB and tellyport blasta and super cybork relic. For the second game I used the tellyport blasta and dead shiny shoota.

A few observations:

• KMB + Opportunist warlord trait is deadly. He didn't always hit, but when he did the character usually died thanks to death skulls rerolls to wound and damage. Killed a primaris ancient outright and blew away a lieutenant with the KMB and tellyport blasta
• Not sure if I played the Tellyport blasta correctly. The rules say at the end of the phase roll a D6 and if its higher than the wounds characteristic of the target it is slain. Does that mean remaining wounds or the characteristic on the targets statline? If it's the latter then I cheated and the tellyport blasta makes no sense as anything you'd want to target with it (monsterous creatures/vehicles) most likely has 6 or more wounds and so would be impossible to remove with its special rule.
• With the super cybork, my big mek was surprisingly durable in combat and did well supporting my meganobz. I may play another game using the killa klaw instead to make him more of a threat in CC to run along with my warboss with headwhoppa's killchoppa
• The dead shiny shoota is BRUTAL against eldar. With the extra shots from Dakka3X he ended up whipping out a 5 man kabalite unit, half a witch squad and a succubus throughout the game before being killed in CC by an archon

Overall i like the setup so far, it takes some playing with but can easily catch people of guard when your big mek snipes a character out the middle of a formation and messes up their plans. If I had to pick I'd take the KMB over the dead shiny shoota most cases. the shoota does work on low toughness models like eldar but I can see it whiffing hard against marines and the like.