Deflationary tokens still haven't got the popularity till date which they deserve. but that doesn't mean game is over for deflationary token. Give this token some time and I can safely say that they will go to moon in coming days. Just wait and HODL.

MASS is popular only because it can be mined on desktop PCs or there is some other cool use case associated with it also?

First rule of crypto is patience, if you buy any token be it BOOM or any other token with intention that it will be at moon very next day or month you are in wrong industry. Buy when it time to buy and sell when its time to sell.

There is fair chance of these coins going up and one can huge profit if deflationary goes up. Those who are willing to take risk right now will be benefited by the first massive jump of this category.

There is an update about MASS that it has touched its ATH of 1.6$ very recently and now its price is stable around 1$. This makes MASS one of most successful coin launched in 2020.

Acceptable blockchains are the one that have the ability to scale as well as the ecological compatibility. MASS is one of very few blockchains that satisfy both these factors.
MASS has built-in cross-chain platform capability from the perspective of a shared consensus network and this has the features of scalability, efficient synchronization of cross-chain communication capabilities and a high degree of network security anchoring physical assets.

An ideal blockchain is one that can satisfy the scalability as well as the ecological compatibility. MASS blockchain is one that can address both these challenges.
MASS has given a natural cross-chain platform from the perspective of a shared consensus network, it has the features of scalability, efficient synchronization of cross-chain communication capabilities and a high degree of network security anchoring physical assets.

The Scalability of the MASS Capacity Consensus Algorithm

The MASS blockchain gives developers the liberty of building their own blockchain by using the interface of the MASS consensus engine. The benefit of this model is that all blockchains built share the consensus provided by the same node network.
In MASS ecosystem, these independent blockchains are called parachains. Every parachain has its own  block generation rules and main chain selection strategy.
The MASS consensus engine solves the problem of non-reusable computing power and unscalable consensus algorithm faced in earlier blockchains like BTC, BCH and BSV.

Reference: https://masscafe.medium.com/mass-the-scalability-of-cross-chain-platform-f2b1b2db1901

Its getting difficult day by day to pick alt coins, since there are thousands of alt coins in the market. Deflationary tokens are in there very initial stages and the supply is relatively high these days. As time passes there supply will go down and chances are that price will go up. DYOR before you jump into any coin. Its just my opinion.