Is the MN Triton reliable? In a word yes!
And no if you find one with an engine that has popped.
You're best to read up on the block surface issue with these 4D56 engines. It's well documented in this forum under the service campaign thread. Educate yourself on this issue so you know what to look for and what potential expenses you might be up for in the future. And also ways to make them more reliable.
In my opinion it's a very serious problem and one that every MN owner may eventually have to face.
Thousands out there that have big kms and never had the issue at all but realistically they're ALL ticking time bombs.
Having said that they can be a very tough engines that can handle a real HP. They respond well to tuning and can support 200hp very reliably.
The rest of the vehicle has proven itself very reliable over the last 10years but like all vehicles they have their limits.. so keep searching this great forum to find everything you need to know.