Want a down and dirty review from an abusive mechanic?
I use the Mastech MS2115B for locomotive work and overall they have worked quite well. We've been using them for probably 6-7 years now and generally get 3-5 years out of each one before they start acting wanky. It's usually just dirty/worn switch contacts but we had 1 fail completely during this time. For the price (currently $86USD on amazon), this issue is acceptable to me. These meters get the living crap beat out of them physically with very harsh hot and cold temperatures thrown in, so I figure they'll break eventually anyway. The display certainly doesn't like being heated to about 150F, but it recovered just fine after cooling down. Oops!
AC clamp metering works fine, and I think DC is fine as well but it jumps around quite a bit. I know DC clamps are hard to get right and I don't have any other meter to compare this to. I usually only measure high DC currents anyway and for that it is acceptable for our use. If it's +/- 10A at 500A it really doesn't matter for my application. With lower DC current its accuracy is questionably, but will at least give you an indication if current is flowing or not.
These claim 750VAC and 1000VDC input rating. I have not carefully studied the inside to see if it's safe or not, and I'm not a qualified judge anyway, but I can say with confidence that I have had more than 1050VDC on these poor things more than once and they did not explode. I have no idea how high the voltage really got, the display just stops at 1050. I absolutely don't trust these china companies enough to hold the unit in my hand with that much voltage on it, especially when my leads are only 600V rated, and I would never attempt to set up this test live. For this specific test I can set it up with the circuit dead, leave the meter hanging where I can see it, then walk over to the control stand and make the locomotive load. Even if it does explode I'd be out of range of the arcs, possibly get hit with shrapnel, and the locomotive will stop loading on its own if something too horrible goes wrong and high voltage contacts the frame. Good enough for 'murica.
I frequently use these on our 110V mains as well and haven't had any issue with that either. Diode check and continuity work fine, but continuity buzzer is slow. Resistance and capacitance measurements are accurate as far as I can tell.
The frequency counter gives me trouble. The displayed Hertz on the Hz setting and on the VAC setting differ dramatically, and measuring Hz from within the VAC setting is definitely more accurate. I never cared to look into why this is, I just know it's a problem and always use VAC instead of Hz. We use the frequency counter to calculate engine RPM based on the alternator frequency so this needs to be accurate to properly set the engine speeds. We should have a laser tachometer for this, but that costs money, and since we're using cheap meters it's probably self explanatory why we don't have a dedicated tach.
It does beep each time you rotate the knob or push any button which annoys some people. For me it's fine because sometimes I bump the rotary switch on accident and I like to be warned when they happens. I really wish it could default to DC without pushing the FUNC button each time. Looks like most other meters operate the same way, so everyone else gets this wrong too. Defaulting to AC is probably fine for most people, but 99% of what I do is DC so this is very annoying. The rotary switch doesn't stop at OFF and can continue to rotate into no-man's land and cause some strange issues so watch out for that.
Next time I take one of these meters out of service for being worn out I'll probably send it into the mailbag and see what Dave thinks about it. It would be nice to get a professional opinion, and since these can successfully handle over 1050VDC they shouldn't be a total disaster inside.