I’ve had the weld on type on 2 cars. The first for over 25 years with NO problems. The common complaint is that they tear out where welded to the frame structure. They stiffen up the suspension quite a bit as they basically prevent the front half of the spring from deflecting under hard acceleration. Mine are a modified kit that was sold by Moss for the MGB and feature adjustable front end-links so I can be absolutely sure that the alignment is dead accurate. They are the same overall length as the LAT weld on traction bars.
I have also fit the bolt on version to a couple of customer cars and have noted that they required a spacer to be installed so that the front eye could clear the leaf spring. They should never be installed loose at the front mounting as it completely negates their purpose, which is to prevent the front half of the spring from deflecting.
Something I had to do on all installations was modify the lower spring mounting plate for the u-bolts. While the axle pad is drilled the correct size for the pin in the leaf spring pack, the lower plate hole is often oversized. This can allow the axle and traction bar mounting plate to shift on the spring pack.
I welded up the hole in the lower plates and drilled them to match the round spacer on the spring pack center bolt/pin. This locks the u-bolts so they cannot shift providing a much more secure mounting point for the traction bars, whichever version is chosen.