Artnovion corner bass traps - anybody know if any good?

Gik looks cheap to me.

well yes.  It is a very low cost option.  The fit/finish is not going to be furniture quality, but the performance is the same.  A tuned membrane bass trap is going to perform about the same regardless of manufacturer.  GIK acoustics is targeted at people who don't want to spend a lot and their materials and manufacturing is all based on that manufacturing budget.  I've worked with GIK traps and they work very well.  It all depends on what you want and how good you want it to look.  The Artnovion are built very nicely and you can tune the bass trap to a specific center frequency.  On the other hand, you can have GIK custom build their tuned membrane to a specific frequency as well (it's just not tunable).

Gik is backlogged several months

That's a bummer.  Sorry.  There are other tuned membrane/pistonic bass traps available, but I haven't worked with them.  The Artnovion might be your best bet, but not sure.  Are you looking at the Sub Trap or one of the normal bass traps?  The Sub Trap is taller and handles the very low 40-60 hz range.  They can be manually adjusted to work best at an exact frequency.  For example, if you tune it to 48hz, it will do 100% at 48 hz.  However, at 40 hz it would maybe only do 50%.  A tuned membrane works extremely well at the tuned frequency, but then drops efficiency at the surrounding frequencies.  However, it is still effective.  The other models handle different ranges, such as 60-80 hz or 80-120 hz.

Acoustic Fields - ACDA-12S. $950 each. Huge 30" x 60" and weighs a very heavy 225 lbs each.  Shipping is probably very expensive due to pallet requirements  Based on the measurement lab results, these are very excellent in the 40-55 hz range and comparable to the GIK tuned membrane (performance is on par).  But again, very expensive.

MSR Inc - Spring Trap.  About $930 each, so it's more expensive.  More complicated to build.  Works best around the 60-80 hz area, but has respectable 50 hz absorption.  Probably not as good as a tuned membrane at 50 hz, but smaller and lighter.  Probably the "widest band" tuned bass trap because it handles frequencies pretty well from 45 to 90 hz, but not as good as a normal tuned membrane at a targeted frequency.

Primacoutic Maxtrap.  Probably about the same performance and results as the MSR, but half as expensive ($420 each).  I don't think these are as good as a normal tuned membrane for low frequency bass.  This is probably because they put a 3" sound panel in front of the membrane so that it's a full range wide band acoustic panel.

ASC (Acoustic Sciences Corporation)  - Iso Thermal Tube Trap $1130 a pair. Based on lab measurements, these do excellent in the 70 to 100 hz, but really don't do as well for the ultra low frequencies (that would be targeted by tuned membrane).

Oh, I figured out that the larger Artnovion "sub traps" are very expensive at about $2,200 each.  That would be $4.2k for a pair.  They are 2.5 x 3 feet (which is larger than GIK), but a heck of a lot more expensive.  They do have a reflective diffuser type front grill, so it would absorb the higher frequencies as much.