i've grown both th seeds heavy duty fruity and serious chronic and would recommend them both i'll start with chronic it's a light feeder that grows fairly quickly and is very uniform from seeds (feminised) it doesn't require any special attention and is easy to grow, it's also fairly low odur in comparison to most of the other options out there. the high is definitely a nice mix with a little couch lock and a sativia high i found it good to smoke any time and sort of suites all needs. the downside i found was that chronic isn't very mould resistant and unfortunately some of the plants i took clones from took forever to root but some were fine and rooted well, the yeild was good with great buds that have great bag appeal once dried has a mild smell with a soft sweet undertone and very crystal covered helping the appearance.
the heavy duty fruity (reg) is a heavy feeder that grows rapidly you'll have a pheno hunt on your hands as the variation is massive not so much in appearance but in height during flower, cloning is easy and fast every hdf i cloned rooted fast, it's a very hardy plant that's mould resistant that grows itself, the stone is very indica (couchlock) and pretty potent you won't get any complaints it's not the best for crystal production but makes up for ot in smell it really does stink and has great bag appeal, which is also part of the downfall it really does stink and seems to consume any area with it's stink that smells more piney fuel like than fruity imo but many people will describe the same bag differently it's kinda hard to put your finger on? the yeild from heavy duty fruity is better than the chronic imo once you've found your mother plant, i really would describe it as a cash cropper!!!!
i grew both the chronic and the hdf side by side in the same environment and the same lights (2x600w hps) i have no true comparison regarding the yeild of the 2 strains as i was experimenting with both (soil vs coco) (standard 3gal pots vs 3gal air pots) and also ditched a few hdf due to the monsterous stretch some of the pheno's displayed, overall i prefered the stone from the chronic but kept my best pheno from the hdf for the reasons above, 4 hdf plants vegged from clone for 3wks to a height of 18 inches in 3gal pots of soil then flipped for 9wks will give between 20 and 24 oz under a 600w hps with very little work in my hands so i imagine that a seasoned grower well versed in training etc could turn hdf into a big production plant.