Such outdated and semi ancient devices, be it iPhone or Android may die anytime unexpectedly and cause a lot of inconvenience during urgent and important times. Phones have maximum 2-4 years useful life.
Even though i can buy used phones on 3 months no question asked money back guarantee (in case of issue), i still would not buy one as my daily driver, be it iPhone and Android and would not recommend either.
Reliability and durability is most important for me, which is why i prefer and recommend new stuff, as the probability of new set going bad is far less than a 2-4 years abused set.
Getting original batteries for obsolete set is impossible, so no matter what, it will become nightmare due to terrible battery timings anyway.