I personally think they rock!

Below is the product of a T5 (4 - 4 ft.) grow. 6 weeks of veg under 4-6500K "cool white" bulbs and currently under 4-3000K "warm red" bulbs. The photo was taken 18-19 days into flowering.

The strain is G13 x Diesel.

2 gallon pots (going to switch to 5 gallon in a few days).

All Fox Farm products: Ocean Forest soil (started seeds in Light Warrior); Grow Big, Big Bloom and Tiger Bloom nutes.

I keep the lights no farther than 5 in. from the tops at all times, and the lights are so cool that I never worry about or have had any problems with burning.

I've heard about diminished yield with T5s but so far everything looks good... but we'll see.