I've had mine since February. I did not get the extended warranty from Musician's Friend. My experience with Line 6 gear over the years has been very positive. Nothing has failed and I've hauled a lot of it out for many gigs.

My biggest worry was protecting the outside of the unit during transport. I purchased a Line 6 amp cover from Sweetwater (it is actually built to fit a Spider IV 75). It is an extremely tight fit but it gets it to the gig safely.

I am not into the extended Warranties myself so I can't really comment on that other than I don't find them useful for myself.

Anyway, in terms of the build quality I think the DT25 might be their best one yet. AX2, Spider2, Spider Valve MK1, MK2, Flextone IIIXL, DT50 and DT25...I have the head and cabinet. Very clean finish, nice piping...I have all of them minus the AX2...The guy who has the AX2 now is still enjoying that amp...I have been very lucky and have only had to do normal maintenance. However, I might mention that I never run my gear without a regulator on the power. In terms of the build the DT25 head is totally solid. The swtiches, pots and jack have a very solid feel and seem like they would last. I have had the DT50 going on two years now and it is has held up very well. The DT25 is basically the same amp in an EL84 version...

The one thing I suggest to anyone that wants to protect thier gear from failure is to always run with an AVR in the power line. I use a Tripp Lite LC1200. A Furman AR-15 is fantastic but costs a lot....Tripp Lite is not as precise, but has a slightly wider operating range (80-140)...Low voltage conditions causes wear on gear...Can take years off it in seconds...The digital gear is very sensitive to this..A tube amp can typically cope with varying input voltages as it is just inherent to the analog nature....The primary reason to have an AVR is to prevent dropouts. I learned this back in the 1980s when I started using an ADA...This is something keyboard players have known about for decades, but this can be new territory for guitar players...If the input voltage drops low enough, a digital device with reboot...That causes a dropout...If input power is regulated so that your gear always sees 117v regardless when the house power is dropping to 80 volts everytime the beer cooler turn on, kick drum hit or the light guy turns on all the ACLs in the house...not only keeps you from dropping out, it protects your gear...mainly the modeler...anyhoo, that's my 2 cents...