Experience With Linear Tracking Turntables

There are so few because there are no benefits! Read your question again: 

But if is such a good thing

That is the question: IF! IF it is such a good thing then yes. But is it? Since when? It looks good on paper. That's it!

On paper a pivoted arm is never tracking except at two infinitesimally small points as it moves across the record. If tracking error was such a big deal then everyone would hear it, right? Right? So then there would be comments all over the place from people, "I hate records because the distortion is so high at the beginning, and in the middle, and at the end, and it only sounds good for like a fraction of a second."

So I ask you, where are all those comments? Where are there ANY comments from ANYONE saying ANYTHING about how this bothers them? Not the geometric theory part. The actual hearing part. I'll tell you: NOWHERE! Tangential arms are a solution looking for a problem that does not exist. Except maybe in the minds of people who bought into tangential tracking arms.

I own Mitsubishi LT-30. All 15 kg of it.

Having said that, belt became goo and, maybe, it will be replaced at some point. If I can clean the mess it left there.

As far as simplicity goes, it is not simple. Not just a motor, belt (or no belt), platter, and an inert arm with cartridge. This one also takes a regular headshell.

At this point in history, it is a nice novelty, but I do not see, or have heard, much advantage over an ordinary turntable.

"I lucked into this Vertical Linear TT which has conventional and removable headshell."

In fact, some of the linear tracking turntables were advertised as "it can play upright, too". Technics SL-7 (mentioned above) and SL-10 were that way, too.

Technics SL 7 turntable played vertically - YouTube

I own a Holbo air-bearing table. Linear tracking air-bearing arm, as well as air-bearing platter. An extremely great sounding table, relatively easy setup, and the thing doesn’t look like an oil rig. 

The air pump is extremely quiet in operation, no negatives on that point. Really, I have no negatives to report at all with this table. Every type of turntable has its compromises. 

Probably the biggest thing with this type of table is cleanliness, keep the arm bearing tube as clean as possible. I cover mine after I am done playing it, otherwise, play and enjoy. FWIW

Walker Proscenium, Rockport Sirius, Kuzma Airline, Forsell Air Reference, Air Tangent all represent top tier linear tracking tonearms. I know there are very good pivot arms too, but a good air bearing type linear arm is great. I happen to own the Maplenoll Apollo and Ariadne which are air bearing arms. I would not trade my turntable for any other table. 

I only recently came to appreciate the B&O MI cartridge, MMC1.  It weighs only a few grams, and tracks at 1.0g with very high compliance. On my Dynavector DV505 tonearm with a very light headshell on my Lenco, it sounded divine driving my Beveridge system.  Now on my Triplanar tonearm into my Sound Lab ESL system, it also sounds fantastic.  I purchased the MMC1 NOS several years ago, but it sat in its container for quite a few years before I decided to listen to it, rather than to sell it without having heard it.  Now I rank it among the top 3 or so that I have ever heard in either of my two systems.  So this makes me wonder how this cartridge might sound in one of the original B&O SL tonearms on a B&O turntable.  B&O made quality components but with a nod to interior design of that era, which probably is why they were largely ignored by true audiophile cognoscenti.  Too chic.
Also, I am now very favorably disposed to SoundSmith MI type cartridges, since Ledermann is a big fan of the B&O cartridges and started his business as a repairer of them.