There is no clear answer, it depends on what is in the system and injectors that need to be removed.
If the injectors are really bad enough that a dealer or garage wants to do a through the fuel rail/line decline the so called service, this is the biggest profit padding scam on the market today.
Its beyond worthless. They try to sell this garbage if the injectors need it or not, its a pure money maker.
One of the most important pieces of information the mechanic needs to know when servicing injectors is the current draw of the individual injectors.
When initially assessing the injectors for service there are a few condition that must be met.
The injector cannot leak internally or internally, there cab be no internal rust or under the top cap and the injector must be electrically sound.
At that point the injectors can be cleaned, first by cleaning the outside with chemicals or bead blasting on metal ones, the body stripped down and filters removed before going in the ultrasonic tanks.
Once cleaned they are tested in drive cycles the units will see in the real world all the time monitoring not only the spray pattern and flow but the current draw.
This testing mimics the cars ECM, it is not destructive testing. The vast majority of injector failures I see are internal leaks and abnormal current draw.
Some times as they heat up an injector can show abnormal current draw, this is a bad unit. It functions but will usually spray more fuel that the others causing the ECM to subtract fuel.
Some injector models are more prone to this sort of failure than others, I know which ones to look for when I do them, one marine unit had an almost 40% failure rate.
I get them because the engine isn't running right so they get the injectors cleaned only to find out its not dirty injectors but electrically failed injectors, keep in mind these injectors all test good with an ohm meter. Checking the ohms of an injectors basically tells you if it has an open or short but that's all.
Cleaning the injectors through the rail only pushed any dirt that may be in rail deeper in the units, it may dissolve some varnish but that's all, it does not diagnose anything or uncover an issue with a single unit.
There area few things to consider when using an in the tank product for preventive maintenance.
On a older vehicle that uses a steel fuel tank like the one in the OP's car a three prong approach is probably the most beneficial.
Older steel fuel tanks may have rust particles in them, it is very important to keep the fuel filter changed on these.
If the car doesn't see much use then a product that dissolves varnish is probably more beneficial than a PEA based cleaner, this is also true of small engines like lawnmowers, snowblowers, etc.
Follow that with a PEA based cleaner to address any deposits on the intake valves and fuel injector pintel or disc.
On later models with plastic tanks that are used daily a PEA cleaner is the product to use, varnish will be minimal or non existent on these and rust particles are usually a non issue.
I have tested Redline SI-1 over 30K and it does an excellent job of maintaining the cleanliness of the injectors when used every 3K. It will not taint the oil so there is no need to wait till the next OCI. It can also be used a few ounces every tank.
This is my personal favorite, Gumout HM and Techron total fuel system cleaner are also good.
For varnish Berrymans Chemtool is hard to beat, it works very well. A couple of ounces in the lawnmower or other small engine every third or forth tank will keep it running like new indefinitely.
Sorry for the long post but I hope someone finds this information helpful.