Do firms prefer to hire law students simultaneously studying to become Company Secretaries?

No.

CS is useful if you want to go in-house to some very small companies in a small town. It's not useful for a law firm career.

Truth has been spoken. Can't stress any more on the point made.

Small town ? Even Companies like HUL, Nestle, Tata Chemicals etc have same person as CS and GC.

Nope. Most listed companies - including some of your list have separate people as legal head and the CS.

I agree most listed Companies have separate legal and CS teams however Hul, Nestle and Tata Chemicals does have same person has GC/ Legal Head and CS.
HUL- Dev Bajpai (Legal Head and CS)
Nestle - B Murli (Legal Head and CS)
Tata Chemicals - Rajiv Chandan (GC and CS)

You are right.
My apologies - I mixed up on the FMCG company with another MNC from the same industry.

In law firms - No
In inhouse legal teams - Yes

law firms do hire cs+llb candidate for post of associate as well as for internship also.

I wonder why anyone interested in jobs in law firms waste their time with CS. Does not help and no one cares

I WASTED MY TIME DOING CS.
SHOULD I STOP? IT'S TAKING/EATING A LOT OF TIME??

It can look good in Corp teams.

Yes it helps, but not always. In specific teams and situations, it works well. If you can manage it, then i think its pretty useful.

No it doesn’t matter.

If you are looking for a job in a law firm it doesn’t matter much. They prefer you to know the work and the laws well of the specific team and practice area.

However, for any MNC under the compliance team it may help.