: Are complaints of Hartz product being dangerous a cause for concern? I have read a lot of documentation and legal complaints including class actions against Hartz products, namely their anti-fleas and anti-ticks products

First, understand that Hartz sells a variety of different products with several different active ingredients. Searching the National Pesticide Information Retrieval System for Hartz Mountain Company reveals that the company uses the following pesticides in their products (I sorted them by insecticide class):

Synergists with Pyrethroids

N-Octyl bicycloheptene dicarboximide (MGK 264)
Piperonyl butoxide

Pyrethroids

Pyrethins
Phenothrin (sumithrin)
Ethofenprox

Organophosphates

Tetrachlorvinphos (Gardona cis-isomer)

Growth Regulators

Methoprene and S-Methoprene
Pyriproxyfen

Phenylpyrazoles

Fipronil

Neonicotinoids

Imidacloprid

Several companies use these same chemicals, for example wikipedia explains

Fipronil is the main active ingredient of Frontline TopSpot, Fiproguard, Flevox and PetArmor (used along with S-methoprene in the 'Plus' versions of these products)

So the question to ask is really "Are any of these chemicals harmful?" The answer is yes, pesticides are harmful in certain circumstances.

The EPA performed a study in 2009 and determined

While most people use the products with no harm to their pets, the
agency's analysis determined that smaller dogs tend to be
disproportionately affected by some products and that the exposure of
cats to some dog products is a concern.

And

EPA recommends that owners consult a veterinarian about the best way
to protect their pets from fleas and ticks or whether pesticides are
needed, especially before using any product on weak, aged, medicated,
sick, pregnant or nursing pets, or on pets that have previously shown
signs of sensitivity to pesticide products.

In addition they also determined that they should begin

Restricting the use of certain inert ingredients that EPA finds may
contribute to the incidents.

I suspect the "inert" ingredients are the synergists. They have no pesticide properties on their own, but contribute to the affect of pyrethoids. You may choose to avoid products that contain synergists.

Based on this information, when choosing to use a flea/tick medication for your pet, you can take precautions based on these findings:

Read the label carefully for cat/dog use
Read the label carefully for the size of pet you have
Follow the application instructions precisely
Never combine/split dosages, only use the right dosage for your pet
Test a small amount of a new product on your pet to check for sensitivity
Talk to your vet to determine if a flea/tick medication is appropriate for your pet
Research the active ingredients to determine if its a type of medication you want to use

For the last point, The National Resources Defense Council performed a study in 2000 (Poisons on Pets) that noted the use of organophosphates is particularly toxic to pets, children, and even adults. One example they gave is

Dipping or powdering pets with tetrachlorvinphos. EPA determines that
powdering or dipping a single pet with tetrachlorvinphos just twice a
year would, over the course of a lifetime, pose a risk of cancer to
the person dipping the pet nearly six to seven times higher than
acceptable EPA levels. Dipping or powdering multiple pets, or doing so
more frequently, would raise cancer risks even higher.

Most of the organophosphates reviewed in this study have been removed from the market by the EPA, but tetraclorvinphos is still in use (as the trade name Gardona). The authors recommend avoiding it.

The authors also recommended avoiding carbamates (urethanes) because they are chemically similar to organophosphates. None of the chemicals currently in use by Hartz (according to my research at the EPA's site) are carbamates.

Finally, the authors do give some suggestions on safer alternatives to these pesticides:

Easy physical measures alone, like frequent washing and combing of
the pet and vacuuming carpets and furniture, can bring mild flea
infestations under control. Alternatives include insect growth
regulators, or IGRs, which are not pesticides, but rather chemicals
that arrest the growth and development of young fleas. These include
methoprene, fenoxycarb and pyriproxyfen and the popular lufenuron
(Program®). Alternatives also include newer pesticide products sprayed
or spotted onto pets, such as fipronil (Frontline®) or imidacloprid
(Advantage®)

Note: Noeonicotinoids (like Imidacloprid) are suspected in playing a role in colony collapse disorder. In addition, Fipronil has been linked to bee deaths. While this isn't a health issue for your pet, you may want to consider it when selecting a pesticide.

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