Single phase buy a 2P 40kA spec "two module width size"
The 4P "four module width size is for three phase"
Do not buy elcheapo one from china.

At minimum, also go for local brand maxguard
https://shopee.com.my/product/15390731/1108027522

Mau cantik ABB OVR T2, Hager SPM240E, Schneider
https://shopee.com.my/product/386581856/13033166073 or official mall https://shopee.com.my/product/403384113/10169243255

https://shopee.com.my/product/226439918/7961546468
https://shopee.com.my/product/311767359/8524543680

All will work fine
Then order RED BLACK GREEN mega kabel loose cut. 1 meter for each colour.
https://shopee.com.my/product/482509406/13428192556 4mm

https://shopee.com.my/product/129202704/5132067326 6mm

4mm or 6mm see SPD model say what size. But 4mm already can use lah..lightning surge is very high voltage and very low current.

It adds on in the main DB box. Refer 3:11 for the general diagram https://youtu.be/oa_a4HTVqoQ?t=191

Depending on what supply (1 phase or 3 phase), you need some room in the DB box (of either 2 modules width, or 4 modules width).
To create room, this may require moving around some MCB's; or if the DB box is full, a new bigger box preferably with similar layout need to be installed.

Similar layout meaning if currently u are using a 12x2 row (24 slot)
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expand to something like a 16x2 row (or 16x3 row).
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If you expand to a 27x 1 row format
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yes,  it give u 3 more slots space as 27>24
but the problem is I dont think your existing wiring lengths can stretchhhhh that much (mostly it is just nice only, no slack).
Hence if its 12x2 row in the beginning then u need to get something that follows along the same format as the old box.

The SPD still need a bit of kung fu to do properly although its install location is confined to within the DB box.
Technically the connection is the easy part but that's assuming the customer DB box has sufficient space else need to upgrade bigger box and/or remove unused MCB to fit and move out existing MCB as the "wong wai" is closest possible to the main MCB [50cm max = shortest bestest].

https://library.e.abb.com/public/76853add5a...olutions_EN.pdf
pages 19, 21, 22, 23, 30 (see TNS/TT system diagram, Malaysia use TT).
Back-up protection dedicated to the SPD = At bare minimum, SPD must be behind at least the main MCB (for indirect strike/T2).

It is recommended to have another MCB dedicated just for the SPD alone (whilst the main MCB will take care of shorts, but additional one MCB still not expensive to implement) in case the SPD totally failed due to damage (and created a short circuit) after kena too many strikes.

Look at MAX s posting about his  power strip burnt .  possible his TV would have blown if he didnt have a  surge protector .

Lightning /Power surges  are always happening on your power lines hence you need
add  a layer of  surge protection to safe guard  your TV , routers  etc...

1 phase SPD  cost about 200rm .  is cheap lah ...  vs  a burnt TV .

Direct hit on house is rare .  Lighting rods  are for direct hit.
SPD T2  are for suppression  of power surge  on the Line . which is  more common happening.
Power strips like Belkins  are SPD type 3 ,    easy to use  , most are less than 5kA protection.

some statement not true.
After reading up on SPD it seems like it’s recommended especially if your house is on a high point

my answer .    where ever the Lightning hits  high point  any  anypoint ...  the  power surge  gets into the tnb power lines  and  get  into houses  within that area .  the surge is typical in about 20kA  .
1 direct Lightning hits  1 house  but the  power surge  can hit  500 houses in that area. 

the mention electrician  need to go back to School . 

yes 40 kA  is  fine.    mean it can handle  peak 40kA  current  in a surge condition / microseconds.
the clamp voltage is important . lower the better .

look for the ones  with  a  status window.  if it goes dead  the window will turn red. so need to change or replace the module.  my guess is  about 10 years life  unless you get a really big surge.

The RCD may be damaged if RCD upstream of SPD.

Based on ST literature

Therefore, the following is recommended:
1. In general, to install SPDs upstream of RCDs (RCDs installed
upstream of SPDs may operate on the expected surge currents);
2. If SPDs are installed downstream of RCDs, the expected surge
currents to earth should not exceed the immunity value of the RCD.

Based on Hager literature

Should RCD’s be required in the installation as additional
protection or to ensure the requirements of fault protection
are satisfied, then the SPD will need to be installed upstream
of the RCD. Where this cannot be avoided, the RCD should
be of the time-delayed or S-type.

I think it is best to follow the experts rather than experimenting because usual RCD type AC is instant trip, we don't use S type or time delayed in residential