First, "I've seen some people say it is legal to do so but I want a second opinion." This is not a legal opinion. This is only in response to the question "Can you use (TM) on a product that is not Trademarked"?
Second, you did not specify a jurisdiction. Since you mentioned Apple, I will assume USA.
tl/dr: Yes, you can used the TM mark and no, it is not fraudulent.
In the USA, there are three "trademark" symbols, (R), (TM), and (SM).
(R) - (Registered) The federal registration symbol. This may be used only once the mark is actually registered in the USPTO. It my not be used while the application is pending.
(TM) - (Trademark) / (SM) - (Service Mark) - According to the United States Patent and Trademark Office:
If you claim rights to use a mark, you may use the "TM" (trademark) or "SM" (service mark) designation to alert the public to your claim of a "common-law" mark. No registration is necessary to use a "TM" or "SM" symbol and you may continue to use these symbols even if the USPTO refuses to register your mark. Those symbols put people on notice that you claim rights in the mark, although common law doesn't give you all the rights and benefits of federal registration.