Gear groupset advice for 2004 MTB.

Well, that groupset linked won’t work terribly well at all on your frame, as it is “boost” spacing.

For decades MTB all used a standard rear hub width of 135 mm between dropouts, which is what your Spesh will be, with 99% of the time a QR axle.

With 11 speed and discs, in about 2015 or so, manufacturers went to a slightly wider “standard” of 142, and started to use a through-axle (screw in) instead of QR. Gave them a little more room mainly to widen space between hub flanges which helps wheel strength. But there was no real difference in chainline, and components all still fit and worked fine on older frames and wheels.

Boost spacing was an extension of that principle, and a few years ago it was introduced to give more hub width again, up to 148 at the rear and 110 in the front instead of 100, again for more wheel strength. Mainly introduced because enduro type long travel bikes got popular, people started to do more difficult terrain with bigger jumps etc, and needed extra strength.

Downside is that to make drivetrain now work,the cranks are a bit different - the BB itself is the same but the arms are offset further out to get the chain line right and minimise noise and jump.

On a non-boost frame - like yours - and especially an older one with 135 spacing, that groupset will be awful to set up and use, and will be really noisy and wear fast.

It also has an E2 type front derailleur pictured, which won’t fit your frame and can’t be adapted. That’s the mounting bolt format for it. Minor nuisance as a different FD could be fitted but still…

In principle though, you *can* fit a modern 2x11 groupset if you can find one! And that’s getting hard especially these days.

You can’t use 12 speed - wheel freehub is different and cassettes don’t fit older ones.

Worth noting that you can still get parts to maintain your old 9 speed drivetrain. Provided the derailleurs and shifters aren’t actually totally shagged, you could simply fit new jockey wheels, chain, cassette, chainrings and cables and it would likely be fine for years more use. Not necessarily cheap as parts aren’t reduced on sale as much, but still can be done.

I’ve got bikes with everything from old 90’s tech 8 speed through to an 1x11 speed boost frame and in all honesty, the 8 speed shifting with new bits is perfectly reliable and functional and easier to maintain.

Just learn how to set gears up yourself. its not that difficult.
All bikes dont change gear well if set badly. The derraileur hasnt changed in principle since the 1940's and indexed shifting popped up in the 90's.

I have 11 speed on a bike with similar frame.
Some of my components are the same as those in the groupset linked to, but my front chainset is a 2x11 non boost XT FC M8000 rear cassette XT CS M8000 11-42, SLX equivalents would be SL M7000. Shimano stuff with an E in the model id means it is over built to cope with heavier use by E bikes.
But really if your components and presumably cables too are new then you have nothing to gain, as others have written learn how to set up your gears or take it to another bike shop to have it done.

Why don't you try a ZTTO groupset 1x from Aliexpress ?