they will work just not as great as you probably hope, they just dont have the penetration or lumen out-put
but that being said sometimes you just have to use what you have
i used a 2 bulb t12 for seedlings and it worked just fine for me but wish i woulda gotten my t5 alot sooner
the cfls are honestly the way to go save money on not running the t12 and run cfls the whole way and you will be alot happier imo! i was so skeptical about cfls when i started and now...... wouldnt choose anything else besides my t5ho 4 ft 8bulber <---- love this light mixed with 6x105watt cfl 2700k, 4x68watt cfl 2700k plus my t5ho im running over 700 watts and for my four plants they just eat it right up