These things are a real steal considering the world they open up to you if you love frugal lens photography!

The quality feels very good, had much worse. Nothing wobbles and sits very firmly on the lens and the camera.

As a Sony shooter since the A7 was first released, I also started collecting Minolta vintage (60's and mostly 70's) cameras and lenses such as the SRT, XG, XD and X series cameras and second gen MC and first gen MD Rokkor lenses.

These are sensational, compact, sharp lenses with character. A lot of modern glass just tries to be sharp while abandoning any attempt to add character to the images... Both have their place of course, and this adapter allows me to pick and choose what kind of images and lenses I want to shoot on the A7RIII and A7RV digital bodies.
It makes high quality vintage lenses a really good value purchase for those who want to slow things down and shoot some manual shots with some lovely film-like character.

The quality of the images are more to do with the actual lens and skill of the photographer so no point giving an opinion on that.

Positives:
The adapter itself seems really well made, well finished and solid, and they have attempted to make the aesthetics match vintage lenses and the body itself really nicely. It does exactly what it's supposed to and does it well at a 'reasonable' price.

Negatives:
There is a little pin/knob which must be lifted/compressed to secure and release the lens... But this little knob is positioned on the grip side of the lens. A7 cameras can be cramped in that area anyway so having a sharp little knob there isn't the best. However, it would be even more inconvenient if it was on the other side due to manually adjusting lenses, so I guess it's mostly unavoidable.
The orange band around the adapter which is supposed to match the Sony mount doesn't 'really' match. It's a slightly different colour and a different finish but it's a nice idea so credit for trying!

It has met expectations

Solid and compact to use with an m42 mount with no problems but only one bottle for two.

Thought the shape would be okay, but lenses with old dots can be used without problems. Good

M42 to SONY E-mount camera connection.
I have the purely manual adapter of the fourth generation. It also seems just as sophisticated.
Due to their design, older analogue and digital SLR cameras have a greater distance from the sensor or film to the flange focal distance of the lens coupling than modern mirrorless compact or even full-format cameras.
This adapter is therefore theoretically just a tube with the corresponding camera and lens connection to restore this distance. There is no mechanical or electronic transmission of lens data and no lenses whatsoever. On one side there is an M42 thread for holding the lenses, on the other the SONY E-mount bayonet connection for the camera. The length (the flange focal distance) is obviously perfectly adjusted, so that I have been able to use all lenses in the full focus range without any loss of sharpness. Internal reflections can be ruled out with this generation, as the matt black interior is very finely grooved.
The adapter from K&F Concept is made entirely of metal and is accordingly heavy. This also gives it a very high-quality and solid feel. The thread is very clean, burr-free, fits perfectly and is well made. There is no play or jamming here.
The orange-copper colored ring corresponds perfectly visually with the E-mount connection on SONY.
The E-mount connection also fits perfectly. It clicks into place well and then sits firmly and completely free of play.
The groove structure on the outside of the adapter makes it very easy to grip and can be connected very easily even under adverse conditions. The coating and even the labeling are very high quality and will certainly last a long time.
The adapter is very well packaged and even comes in a high-quality resealable plastic box. I made an insert out of dark foam so that I could also transport the adapter in the box. Unfortunately, only bubble wrap is included here. A small, sturdy fabric bag can be used in the camera backpack as an alternative. Perhaps an idea for "5 stars plus".
I admit, I initially wanted to buy a simple adapter to test. Now I'm glad I chose this one. At the same time, I have now favored the corresponding “K&F Concept” accessories.
Impeccable workmanship.
Highly recommended.
The trend is towards a second adapter.
This means I can leave the adapter permanently on frequently used M42 lenses.

I HAD NO PROBLEMS SETTING THE BODY, I WORK IN MANUAL MODE

Simple and effective. It works out.

The adapter looks and feels high quality. It is adjustable with small Allen screws and works perfectly.