It is a very good addition, as it gives a good boost.
It is very doable to complete the unlock of this module in 1-4 evenings (depending on how much of the non guardian stuff you already have, how long time you can play etc). Of course some preparations is needed, like having a suitable ship outfitted for a "speedy" trip out to the Guardian site. A basic D-rated ship with A-rated FSD and SRV hangar is all you need, and this is doable in just about any ship.
A very cheap Hauler without engineering, with an Advanced discovery scanner (free honk money for every system visited), will set you back 1.8 Million, it will do ~25 LY (If doing some Engineering G3: ~33LY / G4: ~35LY / G5: ~38LY)
If you do not like the long travel, you can skip the Advanced Discovery Scanner, and honking every system, and then complete the Guardian Puzzle for the neede blueprint, and collect all the needed guardian Material, and then self destruct, and you will back in the station where you started your journey. This will set you back ~240k for the ship , and then ~12k for the rebuy. ut save you the time to travel back home... It is an option, if the long travel distance to a Guardian site is discouraging.
Going up a few steps, Diamondback Explorer, is 8.6 million and will do ~36 LY (If doing some Engineering G3: ~48LY / G4: ~52LY / G5: ~55LY)
So even low grade FSD engineering gives a very noticeable boost. And as seen by the numbers, even the G3 is give you some very nice improvements too.
So what effect will an Guardian FSD Booster have on ships, lets take the two above ships, without engineering?
Hauler
Size 1: +3 LY
Size 2: +5 LY
Size 3: +7 LY
Diamondback explorer
Size 1: +4 LY
Size 2: +6 LY
Size 3: +8 LY
Size 4: +9 LY
These increased FSD range are ABSOLUTE numbers, meaning that the boost is added to your existing FSD range, after engineering etc are factored in. So it does not matter if the ship is light as feahter due to all the engineergng you ahve done, or heavy a rock, due to all the heavy duty enginerring done, the Guardian FSD boost is always the same for that ship.
So even a lower level of these Guardian FSD Booster can have a very noticeable effect on ships with low jump range.
Last example ship, an A-rated Type 9, with a class 5A shield, to protect against accidental bumps in the station etc. I know that not all modules need to be A-rated for this, and w remvoe weapons, utility modules etc, just to keep it simple.
Without engineering this ship will get an empty jump range of ~19 LY, and with full load of 752T cargo (smallest slot is empty), this drops to ~11.5LY
Empty: ~19LY (no cargo)
Full: ~11.5LY (with 752T cargo)
Now adding a Guardian FSD Booster
Size 1: +4 LY (why use a size 1 when the slot is size 2!)
Empty: ~23
Full: ~15.5 LY
Size 2: +6 LY
Empty: ~25
Full: ~17.5 LY
And we are only giving up 4T cargo for 6 LY extra jump range, under full load that is a massive 50% increase here!
And if we combien this with some FSD engineering...
LEts jump directly to G5 with mass manager experimental effect.
Without Guardian FSD Booster
Empty: 30.5LY
Full: 18.5LY
With Guardian FSD Booster (which stil give a flat +6 LY)
Empty: 36.5LY
Full: 24.5LY
I am deliberately staying away from the most expensive ships, and all the min/max builds with engineering etc. Just trying to show with some easy examples, what the effect the Guardian FSD Booster gives.
So this will allow us to bring just about any ship with engineering and a Guardian FSD Booster to have atleast 25LY jumprange, which in my experiance is a very doable jumprange to move around in the bubble. And in many cases you can get past 30 LY, and now that is not bad at all. Of course this is no match for the dedicated bubble taxi builds of Diamondback Explorer/Asp Explorer/Anaconda ships. but with these, you must plan ahead, and wait for the other ships to arrive, as compared to be able to move around with the ship you want to use at your destination directly, so no more waiting for the ship transfer to complete.