Private key to mnemonic words, is it safe? Is it safe to do the following?

Suppose I do not want the HD wallet, but I do want the convenience of using mnemonic words to remember the private key. I know I can convert the private key's hex representation to byte format from which I can get binary format, from there I can follow BIP-39 to generate 24 words that are represented by that private key (because general addresses are used by randomly producing a 256 bit word which is equivalent to 24 words). Can I now use these "mnemonic" words to remember my private key, and completely disregard it (since I can always use these words to get back to the private key). I guess what I am wondering is whether there are cases where different private keys can produce the same collection of 24 words.
Here are two mechanisms for converting a 256-bit (64 hexadecimal  characters) seed into a Electrum seed word mnemonics, and back again.

#1 JavaScript-based

#2 C++ - based

However, the command line interface example below, using mechanism #2, uses one of the most unsafe private seeds is used for demonstrative reference purposes only.

1% echo -n "0000111122223333444455556666777788889999aaaabbbbccccddddeeeeffff" | ./bytes_to_words

rover akin begun nifty laboratory point injury upper eldest enjoy gotten suffice batch snake hospital veteran eagle weird sieve podcast mighty oozed bimonthly biggest upper

2% echo "rover akin begun nifty laboratory point injury upper eldest enjoy gotten suffice batch snake hospital veteran eagle weird sieve podcast mighty oozed bimonthly biggest upper" | ./inverse_mnemonics

0000111122223333444455556666777788889999aaaabbbbccccddddeeeeffff

The results are repeatable using mechanism #1. 

BIP 39 doesn't require invertability support (analogous to ./inverse_mnemonics for Electrum words) albeit it can be accomplished. See How to generate a valid hash for a bip39 seed phrase? for an approach for accomplishing this task. 

The mapping back to the BIP 39 root seed in hex is guaranteed to be unique. However, due to normalization associated with ed25519 cryptography, not currently used by Bitcoin, it is possible to have multiple two sets of 25 Electrum words that map to the same functional private key.