I had a Valkyrie with the MT straight axle conversion, the only problem I had was self induced. I twisted a couple of drive shafts by hot-rodding... then MT came out with their new drive shaft and I had no more problems. I now have an '07-1800 MT Adventure IRS, ridden 20k miles in the last year with no issues.
MT made two styles of conversions for the 1800, SA & IRS. You'll just have to look to see which it is. If you remove the right side cover & look at the front u-joint, if it's green it's the new heavier duty style.