the Altus shown will be a direct swap with a TX-35, etc. "big pulley" tourney RD... if the tourney you're replacing has Small pulleys, you might need a longer chain... if the stock chain has yet to be replaced, i Highly Advise doing so ASAP.
I've also had great response using the Alivio Derailleurs to replace tourneys...
the Altus is one i think of as a "problem solver" choice.... I've had a couple bikes that refused to work right with a Deore or XT, and installing the altus had everything suddenly working smoothly! and a really badly welded Trike(hanger TOO FAR Forward) suddenly was able to shift with an Altus like the one in the pic, and a better chain...
most cheapo chains exhibit excessive side slop, and that slop causes sluggish shifting...
the standard Go-To New chain for 6-7-8 sp. drivetrains is either a KMC x-8 or a SRAM PC-830. Both work well.
there are "upgrade " models of both available... i try to use the nickle plated ones if the budget allows.
Shimano chains (CN-HG71) also work very well. and tend to last 30% or so longer. IME