Bank guarantee is if you put bond money up front. You deposit $ in a bank, but it is frozen until the bank guarantee expires. You will be asked to set the BG for a period roughly equals to your contract. If you leave early the company take your $. When the bank guarantee expires your $ is released to you by the bank.
Or you can do it through "monthly deduction", then you do not need bank guarantee but you have to sign a note promising you will pay the bond amount (they use the term "training fee" or similar not "bond"). Technically it is not a deduction, they lower your base pay until the bond is fully paid, guys pay up front have higher base pay since they paid the "bond" up front. Give you back the $ at the end of contract.
Difference?
1. It affects your base pay therefore differences in bonus and your 13th month salary (both base on base pay) before the bond is fully paid.
2. The legal ownership of the $ before the contract completion.
3. Risk is relatively high for new guys to pay up front if they fail the training. To be fair, the company never fail people on purpose for this money.
Hope it helps.