SPT has an excellent reputation. I've been happy with Cole Tech tubes (always factory fresh and exceed rated power), but if Cole Tech disappeared, I'd definitely buy SPT.
That's a honkin' tube! Integrated alignment laser is a nice touch. My advice on your build is: Don't skimp on the power supply and unless you're doing active cooling, go big on the coolant reservoir - like 10 gallons. I was burning through a cheap chinese power supply every year or two until I bit the bullet and bought a quality one.
I just finished a ground-up rebuild of my diy laser. Doubled the work size to 20x40 and re-designed the gantry using OpenBuild V-Slot. A lot of the work I do involves engraving so getting X speed up was key. I'm running 1,000 ipm now and could probably go quicker if I upgraded the CW230 stepper drivers.