The traditional vaccine is produced using dead Covid19 virus to stimulate your body to produce antibodies to destroy the dead virus. After this phase, your body would be able to recognise a Covid19 virus and repeat the production of antibodies to deal with it. It is a simple tested process. Dead virus would not harm the body system.
Why mRNA is a bit more dicey? The mRNA, m stands for messenger, is not dead virus. It is a part of the Covid19 virus, virile, and when injected into the body, the messenger will activate the body to produce more mRNAs, simulating a Covid19 attack. The amount of mRNA produced by the body is variable depending on the individual. When too little is produced, the body may not react and produce enough antibodies to deal with the attack., thus rendering the vaccine ineffective.
When sufficient mRNA is produced, in simple terms, the normal reaction, the body would produce the necessary amount of antibodies to kill the mRNA and after that the body would be ready to tackle any Covid19 virus attack. The body is thus trained and immuned in a way from Covid19 attack.
The problem is when the body produces too much mRNAs. When this happened, more antibodies must be produced to kill them off, causing great stress on the body system. Some may be able to recover from this, some may not.
Another problem is, what if not all mRNA were killed off? RNA and DNA are basic building blocks of cells and could freely attach to each other, a bit here, a bit there, leading to new DNAs. The permutations and combinations are infinite though the chances are very small. What if it happened, and with millions of people being injected with mRNAs, surely a few may get into this complication. Then the origin of the mRNA becomes an issue. What animal was used to extract the mRNA? The new DNAs could have parts of the DNA of the animal. Then sci fi fiction may come true. No one is sure about this as Nature has a funny way of finding its own way to reproduce itself.
The mRNA vaccines thus has two processes against the traditional vaccines that only reacted to the dead virus to produce antibodies. One process of the mRNA is to stimulate the body to produce more RNAs. Too little or too much would not have the best results. Too much could have too much problem, too little have too little problem.
The second process is for the presence of RNAs, technically would not lead to Covid19 infection, to activate the body defence system to produce antibodies to kill them. When too much RNAs were stimulated, proportionally more antibodies needed to be produced and this may cause too much stress, depending on the individual. Older folks may not take the stress well.
The third part, not part of the process, is the possibility of RNA bits fusing with the body DNA bits. This can be considered rare but not totally impossible. This could become another problem. The result of such a combination could only be seen, unfortunately, over a longer time phase.
So, I would opt for the traditional vaccine, even if it would come later. Singapore's situation is fairly well controlled and we are not in high risk countries like the USA or India and Brazil. There is no need to rush and no need to try the new mRNA vaccines which were approved for emergency use only.
This is my personal view and why I prefer to wait for the proven and well tested traditional vaccines.