I have had the Boss GT 1000 Core for a year. It is extremely versatile and a bargain at 600$ but it for a noob it took a long time to make a really good use of it. I will offer here some info in case others wonder about it.
On the amp side, it has got all the sounds so to speak, but it is up to the user to dial them in. This is a good starting point to understand some of the quirks. BOSS - The Ultimate Guide to GT-1000
The trick here is that you cannot rely on pre-existing presets or purchased patches to get where you want as you might for a Fractal. This is why the Boss is not ideal for a beginner. The best thing to do is to study the sounds you want and experiment a lot with EQ blocks. It is not an easy or a fast process, but the unit can certainly deliver. I found a lot of the pro presets disappointing. Who knows what and how was “lost in translation” but they all sounded off to me, usually for being muffled but sometimes for being too bright, too compressed, etc. We are all different.
As far as speaker simulation goes: The AIRD tech in the 1000/1000 Core is supposed to reproduce the whole chain preamp, poweramp, speakers, but I have had better luck using Celestion IRs as well as other third-party IRs.
On the effects side, it has got the Boss models but with less deep editing capability and with, say, one quality delay block plus 4 basic ones so as not to make the DD500 obsolete. As with amps, there is an issue as that you may have had a pedal or see a picture of a pedal and now find more parameters to control in the Boss than the pedal ever had. So, again, the sounds are there but require patience.
On connectivity and switching, it is incredible but, again, there are quirks like finding out how to set the unit to control your amp channels. Assigning multiple simultaneous functions to a switch is fantastic but also takes a bit of a learning curve.
Here is my setup which allows 3 different uses with no plugging/unplugging of cables:
Guitar In
Control 4-5 (not Ctl 2-3!) jack connects to ENGL Fireball 25 footswitch, channel jack
Send 1 to MXR 5150 and ENGL Fireball 25, the MXR is on or off, true bypass.
MXR related patches in the Boss have pre-amp effects
Return 1 before or after pre-amp effects depending on patch, amp vs MXR
EQ blocks
Send 2 to Amp Return to 1x12 cab
Main Out 1 to Studio Monitor 1
Main Out 2 to Studio Monitor 2
control 2-3 jack out to Boss FS 7 switch
So without plugging or unplugging anything, I can use the amp OR the preamp pedal and the amp power section OR any of the Boss Models OR I can use either the amp or the 5150 pedal in W-D-W.
Then within patches, I can switch my amp channels AND change the Boss path from one for the gain channel to one for the clean channel AND do something else all with ONE push of ONE switch. No dancing on buttons while your are flying up and down the fretboard!
It is a great, little, and affordable switching and routing hub with great effects and very usable amp sounds. But it is not intuitive and the software is old school so take your time.
One issue I have not solved is that I had a good W-D-W sound with my starter amp, a 1x10 EVH Iconic, but not now with the ENGL. Since my sound quality in mono is now amazing, this is no longer a big deal but the ENGL kinda seems to overwhelm the Boss for some reason.
Obviously, mine is a home setup.
Now that I have learned how to use it, I would repurchase the 1000 GT but if I had to give up my amp, I would probably still look to a Fractal for replacement.